Taps: an intro?

[Tim Walsh]

Does anyone have an introduction to taps and dies? I stripped/messed up the top 1.5 revolutions of threads on my S calipers. nobody in town had the right tap, except my mechanic measured the wrong size (yes I still trust him). So now I've got an extra 11x1.0 tap and I need a 10x1.0 tap. I ordered the 11x1 tap on mcmaster but I have no clue what I used for the Pitch Diameter Limit. I don't think it asked me for this last time and I have no clue what this means. help?

[Jim Sims]

You probably need a thread restoring tap not a regular cutting tap. Sears sells thread restoring kits (~$50) that contain the usual metric sizes; I believe it contains the 10 x 1.0 size. I'll have to look in my kit at home. Snap-On and others also sell the thread restoring taps. Jim

[Tim Walsh]

thanks. I still don't know what the pitch diameter limit means though. The specifications for that is h1-h4.

[Jim Sims]

Pitch diameter limit is the tolerance range on the threads's pitch diameter; it controls the tolerance grade (thread fit) of the thread produced. "h1-h4" are pitch diameter limits for inch system taps. The metric tap pitch diameter limits are designated D3-D7. For 10 mm to 12 mm taps I believe you want to specify a pitch diameter limit of D6 which will produce an internal thread with a Class 6H tolerance grade which is the nominal tolerance grade. If you want to know more get a copy of "Machinery's Handbook".

[Tim Walsh]

I think that's all I need

[HarryD]

Originally posted by Jim Sims
You probably need a thread restoring tap not a regular cutting tap. Sears sells thread restoring kits (~$50) that contain the usual metric sizes; I believe it contains the 10 x 1.0 size. I'll have to look in my kit at home. Snap-On and others also sell the thread restoring taps. Jim

Jim,

I have a set of ordinary tap and dies. What is different between them and the "thread restoring" type?