CA2038277A1 - Method of pre-setting and controlling the tightening of stud bolts and the like and novel stud bolts - Google Patents

Abstract

ABSTRACT

Novel preset, calibrated stud bolts and spring-loaded nut assemblies with torque-off spline tips for securing structural conduit units and the like, and method of collaborating the same.

Description

2~3~2~7 ~ETHO~ OF P~E~ETTI~JG AND CO~TROLLI~G
TH~ TI~HTE~IN~ OF STUD ~OLTS AND TH~ LIX~
AC~D ~OVE~ SI~U~ so~T5 The p~sen~ in-~en~ion ~ela~e~ ~o stud bol~5 ~ ~or ~cu~ing or as em~ling metal fran~ing ehannels in right-àngul~r and o~he~ con~igura~ions as ~or supporting electrical ~able-ca~ryin~ ~nd distributin~ ~rays ~nd other su~faces; being more particularly direç~e~ ~o novçl concept~
for presettlng and controllin~ th~ de~ree of ~ightenin~ or 'cension that may be applied to such st~d bolt~

~ .
Su~h el~c~ al cahle trays are ~ S~ u~f~I in p~ r pla~ts an~ other buildin~ to oLganl~ th~ cables ~hroughout ~he plan~, and in other ~pplications whe~e overhea~ ~eillng ~u~p~rt o~ ~ables i~ requi~e~, ~r in ~uilding partl~ions;
and ~o~ an~hor~ng in brick ~aces of buildings ~nd th~ llk The ri~ht~ang~lar and other jolnin~ o~ op~n 1~shaped ~h~nnels for con~ruCtin~ the l~dder-like or other skele~al sup~o~t ~tructure for ~uch tray~ and the llke i9 prin~ip~lly ~ff~cted wi~h aid o~ stud holts gen~ lly having h~xagonal "hex" ) heAds ~hat enable the irl~taller ~o t~ghten ~h~ san~

~3~2~

wherer for ~xample, ri~h~ gul~r po~ition clamping plates are ~o secure right-angularly orien~ed channels toge~herr as later m~re f~llly des~ribed in connecti~n with th~ drawing~
of this applica~ion and in current bulletin ~hee~s of Unis~rut Rouse of Bed~or~, England, entitled "Unistrut Bulldlng S~stems" and "Metal ~ramin~ Structure~".
In use~ the ~nstaller manuAlLy tightens th~ hex he~d bolt that p~sse~ th~o~yh the eharltlel cla;~pin~ plate lnto ~he ~pring-hel~ nut inserted within the channel ~ and d~te~mines by "~e~l" and exp~ri~nce the prop~r tightness o~ ~he ~olt .
A major prvblem wi~h su~h ~ssembly techniqu~ ~ how~v~;c, re~i~es in th~ fac~ ~hat i~ the bolt i~3 tightenec~ too much, it can cause the ed~e lips of th~ ~h~nnel, a~ainst which the nut bears, to collap~e, ~u~h th~t the ~h~nne~ s~s its ~t~uctural integrity. Xf ~ on the o~her h~nd, the inst~ r f~ils to tight~n the bolt quite onough, th~ ~h~nnel n~embers bein~T f~s~en~d togeth~r ~an slip or sllde relativ~ to one anoth~r~ causing struc~ural and sa~ety problem5.
Whil~ par~icularly in ~ther application~, bolt~ wi~h ~plined tips ha~re ~en p~oposed ~o ~h~r when a pr~clet~rmined bolt tiç~ht~nin~,~ or tension is ~e~hed, ~uch a~ ~o~ exampl~, o~ the type de~lbe~ in U~9. Pat0n~ No~

3,812,757 and in th~ current ~talo~ue o th~ ~ssignee 2~3~2~

h~rein, en~i~led "~CB Features o~ Hi~h Strength TC~ ~olts", o~ the purpose~ o~ the pres~nt invention, takin~ th~
~esponsib.ility o~ det~minin~ appropri~te bolt ~ighte~er~
to~ally out of the h~nds of ~he installer i~ most impo~ant:
and conComitant ~ith ~he sam~ t~hniques ~or ~eliabl~
~pr~-setting and callhrating the precis~ de~ree o~ h~enin~
inherently in ~he bolt structure, and p~rts locatlon ~dapte~
to permit ready vi~ual ~xtern~l in~p~ction o~ proper ~igh~ening, and ~i~h ~ mini~um n~mber of part~ i~ the bolt-nut ~ssem~ly, are impor~nt.

Obiece o~ Inv~n~ion The p~imary object o~ the inv~n~ion, a~ço~dingly, i~ to p~ovide a new and improved me~hod o ~nd s~ud bol~ s~ u~e for inherently pre~s~ting, calibrating and ~ontxo~lln~ the tigh~ening tension o~ stud bolt asqem~lies, e~ployi~g the ~plined ~ip~ to~ue-o~f ~roove technique, ~ha~ in ~refi constant and autom~ d~si~ed tlghetning ~ in~R1lers ~nd ~ithout interventlon or Yariati~n o~ ~ension by th~ ~
in~taller~ and pa~ti~ula~ly~ ~hough not e~clu~l~ely~ ~s~ul in ch~nnel ass~mbly struat~es an~ ~he lik~o A ~ur~her ~ec~ i~ to p~vid~ nov~l ~tud ~ol~
asse~blies, includin~ ~or more ~ene~l u~e, a well.

, .
- , .. ' . ' ~
.: .
.

2~3~2~7 Other ~nd furthe~ objq~t~ will b~ ~xplained her~in~fter and are more ~ull~ deline~te~ in the appended claims.

Summary In sunlmary~ and froln one of its importank aqpects ~ the inventLon embra~e~ a stud bc)lt ~ith calib~sted tigh~ening tensi~n con~ol &vmprising a ~hreaded ~h~nk of predetermined diamete~ ~or thr~eadey securiny a washer over zln apertured po3ition-cLamp~ n~ p~ate to a condui~ chanrlel containing a sprin~ loaded nut ~lsposed aline~ wi th said aperture at the bolt sh~nk end ~cel~e~ within the channel, the opposlte ~nd of the balt ~hank b~ing provided wi~h d splined ~ip of l~sq~r diameter ~h~n ~id pr~de~ermined ~iame ter extendin~
f~om a torque-o~f groove colla~ ~h~ dia~e~ o whioh i~
adjusted to ths de~lred ti~h~enin~ tension, ~nd with one o~
a he~d or fi~rther nut ca~ried by ~he bolt ~hank between ~aid ~orque-o~ groove ~n~ s~id wa~her, Pre~er~ed ~n~ be~t mode ~esi~ns and nlethod o~ applica~ion are ~desc~ib~d.

The invention wlll now be çxplained in connection ~i ~h the ~ccompanying ~r~wing~ in whl~h ~ig~. 1 and 2 a~e ~esp~ctively ~ide and top elevation~ of a stl~d bolt .
. - . .

.. . ..

2 ~ 7 7 const~u~ted in accordan~ wi th the invention:
~ igs. 3 and 4 aLe lsolnet~ic views vf su~cessive ~teps in the positioning o~ a ~pring-l~aded n~t wit~ln a channel unit Po~ ul~ima~ely recei~in~ the ~t~ld bol~ o~ E'igs~ 1 ~nd 2~
Figs. ~ and 6 a~e ~imlla~ views ~f a pair of ~lght-angularly oriented ~hoLi~on~al and v~r~i~al) c:h~nnels a~out to be secured by the stu~ bolt an :1 p~ln~lo~ded nut of Fi~s. 1-4 ~lth the aid o a ~ight-a~gle t:lalnpin~ o~
j~ining plate or b~acket, l~spectively showing unasgem~l~d and as~embled s~a~s;
FigsO 7 and 8 ar~ isometric vie~ r to Figs. S
and 6, illustratin~ the bol~ ~ensi~ning ~n~ ~he cornplet21y tightene~ and ~p~ine-~hea~d stay~s 7 Fig~ a sid~ va~ional view sisnil~r to E~ 1 o~
a 3impli~ie~ com~in~d stud bolt and ~pring-loaded nUt a~seml~ly, re~r~8~n~ g a pr~er~2d fo~m o~ the in~Jention;
Fiqs. 10 and 11 are re~pec~lvely si~nilar ~o Figs. 3 and 4 but.lllus~rat~n~ the positloniny o~ the a~semhly o~ Figo Figs~ nd 13 ar~ respe~tively simila~ to Fi~s. 5 and t stlowiny th~ ~s~mbllng o~ ~he struc~ure o~ Fig. 9;
and .. . . . ..

- ' ' - . ~
. ~ . , ' ~'" ' ' ' ' Fl~s. 14 and 15 are respectively slmllar to Pigs~ 7 and 8r again, however~ in connection with the s'cud bolt -spring-loaded nut a~embly of Fig ~ -escriptiO~
Reerring to Figs. 1 and 2, the threa~ed sh~nk of a ~tud bolt is shown ~ B h~vin~ an integral ~o-ln~ hea~ H o~
g~eater diame~er~ tape~ing upwardly and lrlwardly at ~ ~ ~nd mergin~ into an int~g~al ~or~ue-o~ circumf~rential r~ce~s~d groove G t~hown p~e~erRbly of lesser diameter than ~he bolt a) having an upper colla~ G', in turn merginS~ in~ plined or ~luted cylindrlc~l tip T oE somewhat leg~r diame'cer still. Th~ torqu~-o~ gr~ove ~ the loca~ion ~40ve whl~h the bolt is kight~ned ~ ~ by ~ on~-way ~atchet wrench WR ~Flg~ 7) sl~ding ov~r ~nd eng~ging and rot~in~ the bolt by the splined tip cylinder T 'co thread the bolt lnto the spring -~oaded nut ~ ~ shorkly to b~ dosc~i.bed in connectlon wi~h Fig~;. 3-~. Th~R is ~hei~ weAkes~ pa~t o ~he bolt, design~d ~ la~r explained, to b~k or she~r of e l~ig. ~).
A~G a parti~lar~ and hereinat~r-desc~ibed inheren~ly pre~t or callbrated da~r~ o ti~htne~3 or tæns~ ing by ~he W~h~h WR~ th~ ~orc~ r~qui~ad ~o~ t~e lnat~ r to ~Urn ~h~
bol~ ~ur~her lnto. ~he nut wlll be ~ ker ~h~n that required . .

- ' '.
.

.
. .

tv twist cf f the tip T, ~u~h that ~he tlp will b~eak 0~
shear ~f~ at the to~que-of~ ~roove G-~. A~ter ~h~ spline tip has thus broken off, th~ ~olt is t~mpe~-pr~of sinc~ the in~tall~r no long~ has a ~y to grab ~he he~d ~ o ~he bolt, since it is round.
Tuxnin~ now to the details o~ the nut N (Fig. 3) i~to whi~h the b~lt B is threade~, th~ nut is of elongated conf igu~a~ion, h~ving its ~entral th~ea~e~ apert~re 2 ~hat r~ceives th~ th~&aded ~hank of the bolt ~ 1anked by a pair o~ transverse g~oov~ ~l an~ G2. Th~ befo~e-m~ntioned cond~it ~ection C that re~eives the nut, sho~n horizontally orien~d, is provide~ wi~h longitudinally extendin~ edge ll~s tu~ned downwardly ln so~ewhat J-f~hion a~ Cl and C~.
Depending fxom th~ ~otto~ sur~ace o~ the n~t N i~ ~ sp~ing S~ ~y pressing down on the nut to ~om~ s the sp~ing S, ~nd ro~ating th~ n~t 90 from its parallel ~ond~it p~ition o~ . 3 t~ its ~ansve~ e po~itl~n vf Fl~ 4, and ~ele~sing th~ ~:p~in~, ~h~ ~rwove~ Gl and G;~ will sn~p up ln~o en~agement with th~ condui~ lip~ Cl and C2 to hol~ the nut locked ~ithin ~h~ c~r~duit and again~ ;rot~ion as 'che ~'cud bolt E~ i3 thrQA~d ~h~ln.
Th~ ~ys~em is n~w ~ea~ for lnstallation ~ shown in Fig~ . 5 ~nd 6 in ~onn~ n with the ill-l~t~ativ~

' ' `. . '`

: , ,.
. : . . . .
: ~ ' 2~3~2~

a~plication to a righ-~-ang~e conduit jun~tion (horlzontal ~ond~lit unit C an~ ve~tical conduit ~Init ~ ' ) . This is e~ected ~i~h ~h~ aid o a position-~lamping pla~e, shs~wn ln right-angle b~a~ket ~orm at P-, h~ving apert~lres or openirgs 1 ~o~ passing th~ bolt ~ there~hro~gh ~nd into ~ngagenlent ~ith ~h~ thre~ded apertu~e ~ o~ the n-lt N, which will be poai~ioned in~lln~ ~Ind~r the b~a;:ke~ pla~e o~?ening 1 ~ith a ~a~her W ~ositioned on top ~he~of, as shc~wn in Figs. 5 and ~, As before expl~in~. the tigh~enln~ of the bolt by engag~nen~ o~ a r~chet wrench W~ ~ith ~he stu~ bolt ~pline tip ~r and ~otatl~n I ~e~ult~ in the ti~htened and joined condi~ion of E`ig. 13, ~ith ~he tip T sheared off a~ thq p~e~t tigh~ening ~ension. T~ pera~on, mo~aover, p~rmi~ 100~ external visu~l in~pe~tion of ~he ~ightenin~
i.e., tip T gone ~t 1", ~i~. 8, ~nd as disting~lish~d ~o}n e~rller dif~er~nt u~s a~ descr~.hed, for e~campl~, in the ~bove-des~ribed catalogue, whe~e the groov~s ~re a~ th~ end o~ the th~e~d and no~ at the h~ad w~th ~he tip, and whe~e op~r~tlon with one-~ay ~atchet~ 1~ no~ ach~ ev~ble . This ~oces~ with a ~ond bolt--nut ~selnbly wi~l, o course, ~e ~peated ~t th~ v*~tiaal lo~ of th~ brac:k~'c A in the verti~l cond~llt unlt C' t~ ~m~ the ~unctu~e.
A~ b~fore e;~plained, a s~gni~i~an~ advan~ this ~3~

te~hnique re~ides in takin~ all ~ the r~ponsibility out of ~he hand~ o~ ~he ins~aller, the wvrker, who h~s ~bsolut:~ly no cont~ol ov~r wha~ th~ tighteness of the holt is going ~o be. Whatever preset or calibrated tigh~ening ten~ion of the ~olt is desire~ -- 1000 lbs., 2000 lbs., etc~ -- thi~ can all be adjus~ed an~ controlled b~ ~ont~ollin~ ~he ~i~meter o the torque-of f groove ~ . ~ine ~ntr~l and variation c:~n furthe~ be obtained by u~e of a spe~i~l lubricant~ a li~ht lu~ri~ant, on the ~h~e~d~ o~ the bolt so ~ ~o maintaln a desire~ rel~tiv~ly constant Eri~tion coef:~icient ~etween the th~ea.~3 of th~: nu~ ~n~ ~olt. Sinc~ radial ~or~ on the ~pline tip of the bolt is ~d to ~lghten ;t, ~
pr~d~termined torque ten~ion relation~hi~ is required~ The m~ineen~nc~ of ~ pre3et and con~tank fric~i~n co~fficlent hetwe~n the thread~ o~ the nu~ and bolt is es~entlal ~ If, ~or ex~mple, ~ ve~y high coe~ficien~ of f~i~tion was p~e~ent, torque would b~ develop~ ~ast~r th~n tenslon~ If, on the other hand, ~ v~ry low ~oe~i~i~nt of ~rlctioll Wd5 p~esent, ~ension would be ~lev~loped a~te¢ th~n torqu~. To give an example o~ ext~e~e~, i th~ threads wer~ nok the ~3ame ~yp~ o~ ~hr~d3 on the bol~ and nut, bindin~ would re~lt, de~teloplng torcaue very rapidly ~nd br~Aking ~h~ ~lp o the b~lt o~f ~e~ore any ~ul~tantial t~nsion could be - ~ ~ - . - . , - ..'' . ' "
.. : , .
' ' ~3~7 applied~ At the other extrqme, i~ a l~b~i~ant were used ~hat substan~ially elimin~ted friction, ~he bolt could liter~lly be tlgh~ened by ~in9er, ~nd ~h~ bolt ~ould ac~u~lly brea~ off altogether before the spline tip becaus~
of the abs~nce b~ re~istance.

In ac~ordan~e With the pre~en~ inverltion, pr~termlne~
tightenin~ control is t~ilored to ~he cu~tomer, the end ~ser -~ d~pending ~pon ~he thi~kness or the ~ize of the channel, or ~he pa~ticular ap~llca~ion~ ~equ~ring m~re or les~
~ension. As before indic~ed, there a~e ~wo ~ignifi~ant ways for cont~olling the pre~e~ tension. ~ir~tr decrea~in~
the si~ of the groove G so tha~ the tor~ue-o~ groove tlp w~ll bre~}~ of~ earlier, or in~ sing the dia~e~ce~ ~o that it s~ill t~ke ~ ~reater force to break it of ~; ~nd secondly ~
varyin~ th~ l~briGant employed ~- ~he ~reater the l~rieity, ~he g~eater the reductlon in ~he ~iction~ The pr6ferred techniq~o is tv control th~ diameter o~ the tor~ue-o~f g~oove ~ employing only one l~br~cant ~ a~ to p~vide only a ~ingle va~iable, and in this manner~ Attalning V~ry~
ef~ective calibr~ion l)f the ten~ion o~ the ~m~un~ o~

tlghtening. Wher~ ~uch ~roov~ diam~r ~ontrol 1~ usedr lt i~ im~rtant, u~the~mo~3, ~o h~ tr~a~ th~ bolt~ so th~
all the bolt~ have ~che ~ame h~dne~s.

.

-'~33~

A~ previously indi~e~, A preeLre~ stud ~ol~-spring nut ~ssembly i~ sho n in Fig~3. 9-15, whe~ein ~he sprin~ nut;
and bol t a~e ~o~me~ in a uni~c~ry s~ruc~u~e, as b~ cold forming, with the ~unction o th~ he~d o th~ b~lt s~rved by the nut ~o~y ill A single-ple~e const~lcl~ion. Th~l~, in ~he embodiment o Flg . 9 the stud bolt B is shown int:esg~ally ormecl b~low ~he thre!~d s~rews with the body o~ the n~lt N(H), with lts tr~nsver~e gruc:ves Gl ~.nd G;~ and depending sprin~ S . ~nalagou~ly to Figs . 3-~, th~ nuk body N ~ ~, thi~
time carrylng the upwardly lntegral bolt B i~ ~itted into the condui~ C (Fi~s. 10 and 11~ and assembled wlth th~ ~n~l~
brack~t plate A and conduit unit~ C and C ' and ~her W --~ut thi~ time with ~ 1'urth~x h~x nut N ' ~hre~d2d over t.he t~p ~ the 4~ lns~ l~h~ wash~r, an~l wr~nc:h tightened in htly di~erent ~ashion; l~ter expl~ined (Fig. 1~), to splin~ tip torque~~ff (Flg. 15) as earlier des~ribe~l~ In this embod~m~nt, th~ ~pline ~lp 'r, in~t~ad of ~in~ on the ~olt head H a~ in Fig. 1, ~ now a'c th~ qnd tupper) o~ the bol~ khreAds, w1~h the rlu~ N(H~ serving ~s ~he ~olt he~d.
With this ~onstru~tion tigh~enin~ the spllne tip T would not engage th~ tightenlny hex nut N ' . So, a pl~netary type w~ench ge~r ~ is employed o~ well-known 'cype, the lnner spring-loaded s~k~t o$ which hold~ th~ ~ip T, while the ~3~

ou~r ~o~ke~ engages th~ hex nut N', permit~ing i~ ~o be tight~ned down on the 4~1t threa~s an~ a~ainst ~he washer W
~nd bracket A. Such ~ wren~h ~hus pe~mits either ~urning the tip coun~erclockwise or turning ~he nut in a clockwi~e dir~ctibn. with this planetAry g~ring, whichever has ~he le~t amount of resi~tance is ~oing to turn. Initially, in ~ightening up, the nut is tig~tene~ bYc~use there j.~ le~s re~ist~nce ~ntil the polnt is reaehed whcre it ~akes a te~ force ~a ~urn the nut N' th~n it does to twi~t off th~ ~pline tip T oE the bolt. At ~ha~ poin~l the inner socket will turn an~ twiqt the ~ip ~ of ~ the bolt B ~t the preset ~en~ion. Again, simple ex~e~nal ~i~ual in~pec~ion a~
T ' ~ ~ig . ~ 5 ~ a~ures that ~11 ha~ been ti~ht~n~d c~rrectly~
With h~at-tr~ated me~i~m car~n ~teel ~tu~ bal~s oF
~bou~ 12 ~m. di~mete~ and with a 25 mm. length th~a~ed po~tion havlng 11-12 ~h~ea~s per ineh, pres~t calibra~ed ~h~arin$~ ~f the ~pllne tip ~ has be~n aehieve~ ~t 4 ton~
with a groove ~ o~ ~bout ~ mm.
Furthe~ modi~ications will occur t~ thPs~ $killed in ~is art ~nd ~uch a~e con31dere~ t.~ ~ll within ~he spirit ~nd ~COp- o~ ~he ~nv~ntlon ~ de~:ein~d 1n the~ ~pq~nde~i cll:im~.

..

.- . - .

Claims (12)

1. A stud bolt with calibrated tightening tension control comprising a threaded shank of predetermined diameter for threadily securing a washer over an apertured position-clamping plate to a conduit channel containing a spring-loaded nut disposed alined with said aperture at the bolt shank end received within the channel, the opposite end of the bolt shank being provided with a splined tip of lesser diameter than said predetermined diameter extending from n a torque-off off groove collar the diameter of which is adjusted to the desired tightening tension, and with one of a head or further nut carried by the bolt shank between said torque-off groove and said washer.

2. A stud bolt as claimed in claim 1 and in which head is employed and is continuous with said torque-off groove collar so that tightening the splined tip will thread the bolt shank into said spring-loaded nut, clamping said washer and plate to the conduit channel, and with the torque-off groove shearing off the splined tip when the desired tension id exceeded in said tightening .

3. A stud bolt as claimed in claim 1 and in which said further nut is employed and is threaded on said opposite end of the bolt shank against said washer, and in which said spring-loaded nut is integrally bonded to the bolt shank end received within the channel serving as the bolt head, and with the said further nut tightening on the bolt shank against the washer, followed by tightening of the splined tip with the torque-off groove collar shearing off the splined tip when the desired tension is exceeded in said tip tightening .

4 . A stud bolt as claimed in claim 1 and in which the diameter of said torque-off groove collar is varied to vary said desired tightening tension.

5. A stud bolt with calibrated tightening tension control comprising a threaded shank of predetermined diameter integrally carrying at its upper end a head greater diameter merging into a torque-off groove collar of reduced diameter from which extends an integral splined tip of lesser diameter, the diameter of the torque-off groove collar being adjusted to predetermine the degree of tightening tension applicable to the splined tip to tighten the threaded shank into a receiving nut before the torque-off groove collar shears off the splined tip.

6. A stud bolt as claimed in claim 5 assembled with a spring-loaded nut for receiving said threaded bolt shank hold within an open conduit channel with the sides of the nut provided with grooves for receiving edges of lips of the channel.

7 . A stud bolt and nut as claimed in claim 6 and in which a position-securing apertured plate is interfaced between the said bolt head and the open conduit channel, with a washer interposed, such that tightening of the splined tip clamps the head against the washer and aperture in the plate is threaded into said nut.

8 . A stud bolt with calibrated tightening tension control comprising a threaded shank of predetermined diameter integrally carrying at its upper and a torque-off groove collar of reduced diameter from which extends an integral splined tip of lesser diameter, the lower end of the threaded shank integrally carrying a spring-loaded nut serving as the bolt head and receivable within an open conduit channel, with the sides of the nut provided with grooves for receiving edges of lips of the channel, and with the diameter of the torque-off groove collar being adjusted to predetermine the degree of tightening tension applicable to the splined tip.

9. A stud bolt as claimed in claim 8 and in which a nut is threaded upon the upper end of the threaded shank with a position-securing apertured plate interposed between the nut and the conduit channel and with a washer disposed between the nut and the plate, such that, following tightening the nut upon the threaded shank, the following tightening the nut upon the threaded shank, the splined tip is tightened about said groove-collar, shearing off the same.

10. A method of presetting and controlling the tension of threading a threaded bolt within an open-channel conduit containing a locking spring-loaded nut for securing a position-adjusting plate along the conduit, that comprises, providing a splined tip extension for the bolt merging from a torque-off grooved collar of lesser diameter than the bolt, adjusting the diameter of the torque-off collar grooves to predetermine the tightening tension where the torque-off groove will enable shearing off of the splined tip, and tightening the splined tip such shear off to control the degree of tension of the threaded bolt in securing the plate to the conduit.

11. A method as claimed in claim 10 and in which the predetermined tightening tension is further adjusted and controlled also in heat treatment of the bolt and/or with variation of friction coefficient between the bolt and nut.

12. A method as claimed in claim 11 and in which said friction coefficient is controlled by applying lubricant to the desired degree between the threads of the bolt and the nut.