SouthBendModel34
Diamond
- Joined
- Feb 4, 2004
- Location
- Metuchen, NJ, USA
I'm puzzling over the markings on an old Starret No. 391 Center Gauge. (The 390 is the same tool, without the temper.)
The markings are a table which is labelled "Double Depth of Sharp Threads" The table entries seems to be TPI, running 4 to 25 mostly even but 5, 7, 9, 11, and 25 are included. Each entry has a decimal depth associated with it.
Why DOUBLE the depth? What method of measurement is assisted by this table? Is it the method using the 60 Degree thread micrometer? The three-wire method? What?
John Ruth
The markings are a table which is labelled "Double Depth of Sharp Threads" The table entries seems to be TPI, running 4 to 25 mostly even but 5, 7, 9, 11, and 25 are included. Each entry has a decimal depth associated with it.
Why DOUBLE the depth? What method of measurement is assisted by this table? Is it the method using the 60 Degree thread micrometer? The three-wire method? What?
John Ruth