4BA thread cap screws in Canada??

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Potashminer

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I am trying to repair some RALS and RAHS Parker Hale scope rings - the cross bolts have been broken. As near as I can determine, the originals are using the BA thread series, size #4 - hence "4BA". I can find sources in Great Britain, via eBay, but really choke at $US 20 or more postage for 10 or 12 socket cap screws. So, I am trying to source a dozen or so black oxide 1 1/2" long 4 BA socket cap screws - I believe I can machine the heads to make replacements for the Parker Hale rings. Anyone know of a source in Canada??
 
Although using the correct screws would clearly be the best way to go, there may be another option. Four BA (47.5 degree thread profile) has a major diameter of 0.1420" and a minor diameter of 0.1108"and is 38.5 TPI. A No 6 NF (60 degree) has a major diameter of 0.1380" and a minor diameter of 0.1109" and is 40 TPI. It MIGHT be possible to chase the threads with a No 6 NF tap and use No 6 screws. An M4 with a major diameter of 0.157" and 36 TPI might be another option. I would consider all options before giving it a try.

By the way, BA screws were widely used in the British car industry, for electrical fittings and accessories and, I believe, in model engineering. British Tools and Fasteners in the USA - New York I believe, specializes in the British stuff. You might give them a try.
 
Any bike shop that deals with old Brit Bikes, will be liable to have them.

Honestly, this is one of those real good reasons to smile and nod, and just order the damn things. Their usefulness will last a lot longer than the postage cost pain.
 
B_noser said:
Although using the correct screws would clearly be the best way to go, there may be another option. Four BA (47.5 degree thread profile) has a major diameter of 0.1420" and a minor diameter of 0.1108"and is 38.5 TPI. A No 6 NF (60 degree) has a major diameter of 0.1380" and a minor diameter of 0.1109" and is 40 TPI. It MIGHT be possible to chase the threads with a No 6 NF tap and use No 6 screws. An M4 with a major diameter of 0.157" and 36 TPI might be another option. I would consider all options before giving it a try.
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Thanks for the suggestions. As it turns out, the 6-40 is the thread used on the Ruger factory rings, and I had bought a package of Torx headed ones to replace the originals that had slotted screws. The cap screws on the Parker Hale rings are also 4BA size. So, I tried to swap them. The 6-40 definitely turn into the Parker Hale knobs - just slightly wobbly but go all the way in for their entire thread length (8 threads) The 6-40 into the Parker Hale ring's bottom half also makes the full 8 threads with finger pressure alone. Then tried the 4BA in the Ruger rings - makes about one thread and stops. I don't have M4 to try, but pretty much confirms that 6-40 could be used in 4BA if backed in a corner, but you would need a 4BA tap to chase a 6-40 thread to swap the other way. I wouldn't be trusting the torque strength of 60 degree screw pitch in a 47.5 degree hole, though.
 
I had to get some for my PH target sights from the American outfit.
The shipping was USD $45 for international express. This was a flat envelope.
However, one of the BA screws will replace the SMLE trigger guard screw when a longer one is needed to mount a Parker-Hale 5A or Parker 9 sights.
The original t/g screw is 37 tpi, and the BA is 36.
As it happenned, I had to fit one up this morning and they mated up just fine.
 
Update. I ordered some socket head cap screws - 4BA x 1 1/2" on Feb. 12 and they arrived here in Manitoba today, Mar. 5. On-line from BA Bolts in U.K. - they charge a flat 2 G.B.P. "airmail" charge for international mailing by Royal Post - apparently includes the Customs Declaration - along with 2.50 G.B.P. for "postage and packaging". No extra charges from Canada Post or Canada Customs. Paid with VISA (through (FRAUD ALERT), although I detest supporting those people!!)

Perfect fit into a set of the shiny RAHS.3 Rings I had here - cross bolt knobs just spun right on.
 
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