Re: What is this item?
The first one is definitely a screw thread micrometer. Typically they use interchangeable anvils (the tips) for different thread pitch ranges. They are for cutting threads on a lathe to measure the pitch diameter of the groove, as this is the only true way to get an accurate read on the groove depth. The way most machinists do it is with thread wires, and standard micrometers, and then look up their results in a table or calculate using a formula, as having thread mikes and anvils for all common sizes of threads is expensive. Most of the time, when you make a thread on the lathe, you try and get ahold of the mating female thread and just cut it to fit by feel.
The first one is definitely a screw thread micrometer. Typically they use interchangeable anvils (the tips) for different thread pitch ranges. They are for cutting threads on a lathe to measure the pitch diameter of the groove, as this is the only true way to get an accurate read on the groove depth. The way most machinists do it is with thread wires, and standard micrometers, and then look up their results in a table or calculate using a formula, as having thread mikes and anvils for all common sizes of threads is expensive. Most of the time, when you make a thread on the lathe, you try and get ahold of the mating female thread and just cut it to fit by feel.
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