Machining a pump - GIF

[Frank S]

1/2 TPI. Wow. What’s the typical nominal OD for a 1/2 tpi thread?

I don't seem to find the API chart that used to show nominal ODs versus TPI so we might have to try this
Acme threads might be a reasonable way to come up with an OD for a 1/2 TPI, 2 TPI are typical for ODs ranging from 3 to 5 inches this is where my 14th edition of the machinery's hand book stops. it does give the dimensions for a 1 TPI thread but no mention of typical diameters the Same with my 8th edition Marks standard handbook for Mechanical engineers. Other types of threads seem to bottom out around 3 TPI with some references to 2.5 TPI
But looking at this another way think of a round grove that is used on larger winch drums called a Lebous grove. The 1/2 TPI would equate to a 2" wire rope and if we were to take half the minimum recommended pulley diameter to be 20 times the diameter of the wire rope as a starting point for a minimum bend radius however 30 to 40 times the diameter of the wire rope is more commonly used in practice for fatigue life, a 20" diameter cylinder would be the smallest the 1/2 TPI would ever be used for