BSF Bolts failing when tightening

[Mark Atkinson]

Hello All,

I am having nasty quality issues with some newly acquired BSF fasteners, specifically that they will not take sufficient torque before stripping the thread. They are ‘R’ grade, which indicates they are supposed to be HT. I have also found the nut supplied with them to have undersized heads, so that they do not work with standard BSF tools.

A 1/4 BSF grade R should be able to take up to 8.2 ft.lbs torque, but these are failing before they are anywhere near that load.

They appear to be from two separate manufacturers LPS and SB.

I am fortunate that I have sufficient feel when tightening fasteners to recognise when a thread is stretching and seldom have problems, but,  made up for that today with several set screws failing during assembly and before I had started to nip them up!

Frighteningly expensive, they came from a recognised supplier of BSF fasteners, who I will speak to on Monday.

This could be a nasty safety issue for someone who has not detected the fasteners weakness.
Please may I ask if anyone else has had a similar experience.

Regards, Mark

[Tony Betts]

Hi mark,

I can't help with the quality of the bolts.

But the metric size head on BSF and whitworth nuts and bolts, has been around for at least 10 years now.

They are normally a cheap substitute.

Perhaps your supplier is cheapening there bolt quality as well.

Perhaps done so they can compete with other suppliers.

I don't know who your supplier is, but I find I get better quality results by going to a main supplier. Ie supplying the trade, and engineering world. Rather than a go between.

Tony.

[David.H]

Hello All,

I am having nasty quality issues with some newly acquired BSF fasteners, specifically that they will not take sufficient torque before stripping the thread. They are ‘R’ grade, which indicates they are supposed to be HT. I have also found the nut supplied with them to have undersized heads, so that they do not work with standard BSF tools.

A 1/4 BSF grade R should be able to take up to 8.2 ft.lbs torque, but these are failing before they are anywhere near that load.

They appear to be from two separate manufacturers LPS and SB.

I am fortunate that I have sufficient feel when tightening fasteners to recognise when a thread is stretching and seldom have problems, but,  made up for that today with several set screws failing during assembly and before I had started to nip them up!

Frighteningly expensive, they came from a recognised supplier of BSF fasteners, who I will speak to on Monday.

This could be a nasty safety issue for someone who has not detected the fasteners weakness.
Please may I ask if anyone else has had a similar experience.

Regards, Mark

 Mark, as a former fastener person....to be a bit pedantic..(sorry)... R or S  indicates the strength (S is close to metric 8.8 I recall) "High Tensile" is a bit fuzzy as a description. The recommended tightening torque is a good indication & if you feel stretch then they could be a bit iffy! I don't have a list of recommended tightening torques to hand...they vary whether threads are lubricated or not, of course.
Mind you we used to break the heads off a 10.32 R quality hex head bolt that was put into an aluminium Rivnut to show that our Rivnuts were more than suitable for many uses! (3/8 BSF aluminium Rivnuts were used to hold the winch onto  a Landrover Chassis in the 50/60/70's!).
I'll see if I can identify LPS & SB. It is normally a good sign if there is a head mark & a strength letter.
What thread size? What A/F dimension on the nuts. As an aside, Stainless fasteners are also no substitute for S grades where there is any significant load (seat mountings perhaps), but probably ok to hold bodywork together!

---

Hello All,

I am having nasty quality issues with some newly acquired BSF fasteners, specifically that they will not take sufficient torque before stripping the thread. They are ‘R’ grade, which indicates they are supposed to be HT. I have also found the nut supplied with them to have undersized heads, so that they do not work with standard BSF tools.

A 1/4 BSF grade R should be able to take up to 8.2 ft.lbs torque, but these are failing before they are anywhere near that load.

They appear to be from two separate manufacturers LPS and SB.

I am fortunate that I have sufficient feel when tightening fasteners to recognise when a thread is stretching and seldom have problems, but,  made up for that today with several set screws failing during assembly and before I had started to nip them up!

Frighteningly expensive, they came from a recognised supplier of BSF fasteners, who I will speak to on Monday.

This could be a nasty safety issue for someone who has not detected the fasteners weakness.
Please may I ask if anyone else has had a similar experience.

Regards, Mark

 Mark, as a former fastener person....to be a bit pedantic..(sorry)... R or S  indicates the strength (S is close to metric 8.8 I recall) "High Tensile" is a bit fuzzy as a description. The recommended tightening torque is a good indication & if you feel stretch then they could be a bit iffy! I don't have a list of recommended tightening torques to hand...they vary whether threads are lubricated or not, of course.
Mind you we used to break the heads off a 10.32 R quality hex head bolt that was put into an aluminium Rivnut to show that our Rivnuts were more than suitable for many uses! (3/8 BSF aluminium Rivnuts were used to hold the winch onto  a Landrover Chassis in the 50/60/70's!).
I'll see if I can identify LPS & SB. It is normally a good sign if there is a head mark & a strength letter.
What thread size? What A/F dimension on the nuts. As an aside, Stainless fasteners are also no substitute for S grades where there is any significant load (seat mountings perhaps), but probably ok to hold bodywork together!

The manufacturers appear to be : LPS Lakshmi Precision Screw Co. Rohtak Haryana India 124001. Big Company, automotive supplier with good branded products. Will certainly have good QC ratings.
SB are closer to home! Smith Bullough in Wigan. They are ISO 9001 approved.
Both should know what they are doing.
Nuts sound more fishy!

[David Cochrane]

A mechanical design engineer once told me that the torque specified for tightening nuts & bolts was for dry threads. Putting lubricant on the threads causes the friction between the parts to lessen drastically, which can result in excessive load on the fastener. Some years ago I had a complaint from a customer (who really should have known better) that he had wound the end off one of my halfshafts when tightening the castellated nut. Casual questioning revealed that he had liberally applied oil to everything (including the tapers)...

[Chris KC]

David is absolutely right, or to re-phrase it, the torque specified for a joint must reference the assembly condition (dry or oiled); either directly, or by default through a work standard.

In the modern industry 'standard' bolt torques are only for general work; torques for 'important' joints are established by individual tests of a number of samples, joint by joint.

For the vintage car enthusiast this is hardly practicable, and we have to rely mostly on 'feel' and the advice of those who bravely went before us!

[Bob Culver]

Completely dry threads are somewhat impractical., so oily is the more usual condition. This does not mean dripping SAE50 or 140 EP or moly or graphite or any other grease. A hard washer has huge influence An old  Newnes gives 7.5 ib ft for ¼ BSF 45 tsi, the basic HT grade presumably corres to R. Presumably your wrench accurate. Can check using a lever and spring balance, scales etc

It is unusual for the thread to fail before the core, for any strength.

M6 can be mistaken for ¼ BSF.....

[Colin Reed]

Hi Mark,
What are the set screws being used on, are you saying the thread strips on the screw or nut.
I use ARP Studs & Bolts and the stretch  on a 3/8 big end bolt is only 6 thou for max torque and must go back to with in 1 thou  of the length before being torqued when removed other wise it is scraped.

Cheers Colin

[Duncan Grimmond]

I keep a copy of this on the lid of my toolbox as a guide. Note that is is for dry assemblies recommending a 10% reduction for oiled ones. There is a metric one available which I must admit to using more often!

http://electronicfilters.tpub.com/TM-10-...3P_104.htm

[Ruairidh Dunford]

A mechanical design engineer once told me that the torque specified for tightening nuts & bolts was for dry threads. Putting lubricant on the threads causes the friction between the parts to lessen drastically, which can result in excessive load on the fastener. Some years ago I had a complaint from a customer (who really should have known better) that he had wound the end off one of my halfshafts when tightening the castellated nut. Casual questioning revealed that he had liberally applied oil to everything (including the tapers)...

Did the end of the half shaft fail before the threads?

[David.H]

I keep a copy of this on the lid of my toolbox as a guide. Note that is is for dry assemblies recommending a 10% reduction for oiled ones. There is a metric one available  which I must admit to using more often!

http://electronicfilters.tpub.com/TM-10-...3P_104.htm

The plating on bolts & sets etc also affects the tightening torque. Most basic testing would have been done on unplated fasteners as that gives a known reference point. Cadmium plating is "slippier" than the zinc (with clear or yellow passivation) that generally replaced it (less toxic, but also less corrosion resistant) and so test results should say what state the fastener was in.
The point about M6 & 1/4 BSF is well made....1/4 UNF with 28 tpi have been known or "persuaded" to almost work...