Seat and Thwart screw size

Don Sable

Curious about Wooden Canoes
I am restoring a 1921 18' CS grade OTCA. I am trying to replace the steel seat and thwart screws. Measuring the screw size I find that they are #12 (.215" Dia) and 22 threads per inch. This is not the present day standard of #12-24UNC thread size. Was the #12-22??? the common screw size in the 1920's when the canoe was built? I will probably replace with 12-24UNC's. Comments?
I can tell you that a Standard was not adopted for screws threads till much latter. I can't remember if it was 50's or 60's. But I want to say it was early 60's. Before that there were many different sizes and thread combo's.

I restored a lot of old wood working machines for my shop and we never tossed old bolts!! You never knew when you would run into a old one that you couldn't pick up locally.
The '21 Otca that I just finished used 12-24 screws and nuts (Jamestown Distributors). I've never found, (not that they don't exist) a 12-22. I worked in the fastener industry for over 30 years and never encountered a 22TPI screw or bolt. Standards for fasteners were developed in earnest and widely practiced by the mid 1800's. That's not saying that some fly by night wasn't turning out 12-22's or out of tolerance 12-24's. Anything is possible there.... but doubtful in my mind. I have found damaged threads that had to be chased with a tap. Often they were broken off below the nut after installation. That serves two purposes. First it removed the extra shank material when a "too long" screw was used. The other thing is that when the screw is broken off it boogers up the threads so that the nut can't work loose.


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Thanks for the quick reply. I agree. I think the screws were just manufactured with loose tolerances back in the 1920's. All of the screws on my canoe matched the 22TPI thread gage whereas the 24TPI gage was a slight misfit. I will replace as you did with 12-24UNC screws.