Identifying a thread

[DPittman]

Okay I started with my Machinery's Handbook and sort of got overwhelmed.

I think it is an acme thread with 8tpi.

Any hints on how to identify a thread without high end measuring tools. It seems to me there are acme, square and "unique" threads that can look very similar especially if they are worn.
Ive never cut acme threads before and this looks like a challenge that Id like to attempt.

 

[Arbutus]

Does't look like a true ACME thread form. Trapezoidal threads have flat shoulders, and the tooth root and tip are the same width

In fact i'd almost say its a worm. What is the mating part?

 

[Loosenut]

Could be a badly worn Acme thread?

 

[Susquatch]

My first thought is worm too, but the adjacent shoulder sort of rules that out. So does the lack of worm wear patterns

Next guess is worn acme. But the gnarly look of the metal at the thread roots says otherwise.

So I'm gunna go out on a limb and say that it's a poorly formed acme thread. The thread roots, the rest of the shaft surface, and the break all suggest that the part is cast. The basic threads were likely cast in too. If so, the surface of the threads were probably cut a bit or burnished afterward to achieve a smooth working thread surface.

Like most threads, you can follow standards to achieve compatibility or a machinist can make whatever he wants. This is a perfectly useable thread but it needs a custom matching nut because the thread profile ratios are not standard.

If you can't find an original replacement, I'd make a new one to match the nut. Forget about casting. Just make a better one out of steel.

Can, we see the rest of the machine where that fits?