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5/16"x 28TPI ?? WTF did that come from?

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PackardV8

Hot Rolled
Joined
Jun 4, 2006
Location
Spokane, WA
I'm well into making a custom measuring jig using a fine old Ames AGD-2 1" travel dial indicator I had on the shelf. I chose it because there is a threaded boss at the top. The plan is to make a threaded adjustable stop which would attach by screwing onto this boss.

No battle plan survives the first contact with the enemy. As near as I can see, it's a 5/16" X 28 TPI and who's got a tap for that?

jack vines
 
PackardV8 said:
As near as I can see, it's a 5/16" X 28 TPI and who's got a tap for that?

jack vines
Click to expand...

There are some Chinese sources on eBay that offer all sorts of unusual tap and die sizes. I recently bought a set of 1/2 x 27 and 1/2 x 28. Makes a heck of a differential screw. I checked and you can get 5/16 x 28. Just search eBay for "tap 5/16 28" and you'll find several sources.
 
Thanks for all the replies. To my surprise, I did find it for sale, but why was that the only and perfect thread for the dust cover on top of a dial indicator? Can't see any reason a 5/16"x 24 wouldn't have been just as suitable.

jack vines
 
And Winchester used 31 and 1/2 TPI, on many of their gun screws.

Much like th apocryphal story about how the width of Roman Chariot wheels relates to the size of the rocket boosters on the Space Shuttle.

Some guy chose it, it got used for that purpose, ever after.

Cheers
Trev
 
To complicate matters, the next few Chicom dial indicators I picked up use a very small diameter fine pitch metric thread on the top collar. Anyone have a spec for that one?

So far, Sunnen uses the largest thread on the top collar, Ames the 5/16" x 28 and the Chinese the smallest.

Whatever happened to the concept dial indicators were standardized so attachments, tips and clamps would interchange?

jack vines
 
I feel ya man. 33 years in the trade and just came across my first 1/2"-12, which I believe was the standard way back when. The only reason I knew what it was is that I remembered reading about it here.
have fun
i_r_
 
i_r_machinist said:
I feel ya man. 33 years in the trade and just came across my first 1/2"-12, which I believe was the standard way back when. The only reason I knew what it was is that I remembered reading about it here.
have fun
i_r_
Click to expand...

The 1/2-12 was a standard about 100 years ago. I have an old Smith Mills machine with some of them.
JH
 
On the plus side they are still in business so you could just call and ask them what the heck old Bliss Charles Ames was thinking when he picked that. They were actually super nice and very helpful and would probably track someone down to tell you.

My annoying thread story was the very first inside thread I ever had to cut. For a B&S horizontal arbor, 1-3/8" - 10 and just to add a degree of difficulty Left Hand thread. Grrr.
 
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