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bobber58 22nd July 2021 16:41

Having trouble finding bolts
 
So I'm working with a Knuckle/Pan rear drum brake. The stock style 3/8-20 bolts won't work with my wheels (custom Invader). The head on them is too big to allow them to go into the holes. So I need 3/8-20 x 1 socket head or button head cap screws (preferably chrome or stainless, but beggars can't be choosers) and cannot find a single source for 3/8-20 bolts anywhere. Anybody have any leads on where I may find these? Thanks.

ryder rick 22nd July 2021 19:03

Never heard of a 3/8" x 20 thread, not at all common. Not listed in my machinists handbook.

Common 3/8 sizes are 16 and 24 TPI

IXL2Relax 22nd July 2021 19:03

Try:

https://www.google.com/search?q=3/8-20+bolt+chrome

https://www.google.com/search?q=3%2F8-20+mcmaster+carr

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bobber58 23rd July 2021 00:51

Quote:

Originally Posted by ryder rick (Post 5906562)
Never heard of a 3/8" x 20 thread, not at all common. Not listed in my machinists handbook.

Common 3/8 sizes are 16 and 24 TPI

Yes, it's not common, but it is what Harley used on early rear drum brakes. Why, I have no idea. It's a British thread from what I can find.

bobber58 23rd July 2021 00:51


All they show is a lead screw. No bolts.

IXL2Relax 23rd July 2021 01:30

Looks like the designation is 3/8" BSF (British Standard Fine)

https://www.asmc.net/3-8-20-x-1-2-ft...l-black-oxide/


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Hopper 25th July 2021 05:29

Quote:

Originally Posted by bobber58 (Post 5906671)
Yes, it's not common, but it is what Harley used on early rear drum brakes. Why, I have no idea. It's a British thread from what I can find.

It's probably not a British thread form. Brit threads are a 55 degree angle on the V of the thread. US are 60 degree. My guess is Harley made their own special 60 degree 20TPI thread so you could NOT use a standard US socket head cap screw in there in place of the original bolts that had a special chamfer on the seating edge of the head to locate the wheel and to stop the bolts working loose.

The wheel hub had matching chamfers on the bolt holes. If your custom wheel has these, you would be best to machine down the original bolts to fit in the space available. Otherwise machine off the chamfer to fit your custom wheels and use Loctite or safety wire to stop them coming undone.

But BSF bolts will fit if you absolutely have to. The two different angle threads will usually screw together ok as they are made with plenty of clearance on mass produced threads. As long as diameter and TPI are the same you are usually ok. No great loss of strength or security involved. Some maybe but not great.

Harley made a lot of oddball threads pre-1970s as they had the machines to make all their own fasteners and parts threads rather than buying in standard issue. But they all used the standard 60 degree thread roller tools.

jeffro57 25th July 2021 18:51

go to tractor supply

Andy Hog 26th July 2021 16:39

Can you not just tap in a metric thread & replace with metric bolts, or are you a bolt specific type of guy?

ryder rick 26th July 2021 18:59

Are those the bolts with the tapered shoulder like lug nuts?

https://cyclevintagee.com/replaces-h...-part-43530-35


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