10TPI Tap Bolts for OLD Challenge Cutter ???

A number of the 1/2” x 1” soft steel bolts (which secure the blade to the guillotine bar) in our 33” 1900s vintage Challenge have stripped. I was reinstalling the blade after our recent relocation, and realized that at three of the seven were not grabbing the blade.
They seem to be about 10 threads/inch.
Unfortunately, the local hardware, and box stores don’t have any such thing.
The US ANSI standard for a 1/2” screw is 12TPI or something.

Does anybody know a good source for such things or will we have to have them machined somewhere, which sounds like a major headache?

We’re sort of ‘screwed’ without them, since our small Challenge is powered by a 3-phase motor, and the electrician probably won’t get to that for some time, having discovered that the 3-phase service coming in to the new location is 440V and we’ll need to find a step-down before we can do anything with it.



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Might be best to re-drill and tap to a common oversize, probably 5/8’s. A lot of early industrial equipment had proprietary fasteners.

I believe I remember that 1/2” standard threads are 13tpi. You could check to be sure the bolts are actually a full 1/2” — if a bit undersize you might get away with tapping out the holes to 1/2-13. You could also consider 9/16 but I don’t remember the tpi for them — that’s an odd size.


Are the threads on the bolts bad or is the threaded hole stripped? or both??

If the threaded holes in the cast iron frame are in good shape or even slightly worn new bolts would be the way to go.

Find a smaller machine shop that does small jobs and have them take 3/4” hex stock and machine them down to the same size or maybe .010”/.020” over size as one of the good bolts. They can use one of the good bolts for sizing purposes.

Drilling and tapping to the next size larger is doable, but you need to make sure that there is enough metal there to do it and you will need to enlarge the holes in the blade to allow for the larger bolts. And unless you do all 7 holes then you have 2 different bolts to deal with every time you change the blade. Not a major hassle, unless you forget.

New machined bolts will probably cost just a little more than modifying the existing ones.


We encountered a similar issue while refurbishing a Washington press - some of the bolts were 1/2” with 12 threads per inch (vs. the standard 13 threads per inch). I found they were British Whitworth threads. I would suggest getting/borrowing a thread count tool and verify the number of threads per inch of your bolt. If yours are actually 1/2” 12 tpi, you can buy new ones from a web site for $1.50 to $7.50 each depending upon how long a bolt you need


The web site also had some background information about the uniqueness of the 1/2” bolts.

“British Standard Whitworth (BSW)

These are the original, 19th Century, coarse-threaded industrial bolts designed to hold locomotives together. Because of their coarse pitch, they are more prone to vibrating loose, so are little used on motorcars. Except for threading into aluminum (e.g. crankcase studs), where a coarse thread is less prone to stripping than a fine one. It turns out that, except for 1/2” (where the British use 12 threads per inch (tpi) and Americans use 13 tpi) the thread pitches for the rest are the same as for American Unified Coarse (UNC). However, the thread form is different; Whitworth = 55 degrees; UNC = 60 degrees. In spite of this, mismatched nuts and bolts mate nicely, so you’re likely to find UNC bolts or studs where BSW should have been.

Good luck.


Hello, all.
Thanks very much for the input.

These are tap bolts threading into the blade. The guillotine itself has seven slots which allow the blade to be adjusted, per usual. The slots are not threaded, of course.

Definitely need to find a thread gauge and confirm the TPI.
We have two blades, per usual, so I’d just as well not have to get all those holes rethreaded.

I sent my business partner to the local hardware, and we got the standard US 1/2-1” which definitely did not work. I think they were 12tpi.

Many thanks, again!

slowprint . com
fraterdeus . com

Can your blade sharpening service tell you what the tpi is?
Maybe they can help locate the bolts also. If they also sell blades they may have resources for the bolts that fit.

just a thought.

If the threads are in the blade, which is probably about 3/8” thick, they may be 1/2-20 fine threads so as to have more threads in the blade. Don’t you have the old bolts you can take to the hardware store and have them check the thread count? Sometimes an odd bolt like that can be matched with metric as well — even though it wasn’t metric to begin with.


Interesting, the amount of extra clues & info, incoming, between, 29th @ 15 55 and 30th @ 14 07.
E,S.P. maybe or a little .>Off Line< help. ???? Good Luck