metric thread classifiction

[xandz]

We're cutting an M4 x .7 metric thread. Print calls for a 6H thread classification. Our normal procedure is to just order a thread gage of the proper classification and check our thread with it. However, we have a 6H gage and a 4H gage and they both have the same size go and no-go pitch diameters stamped on the handle. why would a 4H and 6H have the same limit sizes?

 

[juergenwt]

You sure you do not have a 6H and a 4h? One a thread plug and one a thread ring?
M4 6H internal thread pitch dia. is min. 3.545 and max. 3.663
M4 4h external thread pitch dia. is min. 3.489 and max. 3.545

M4 5H internal thread pitch dia. is min. 3.545 and max. 3.640
M4 7H internal thread pitch dia. is min. 3.545 and max. 3.695
With the letter "H" the min. stays the same. The 4 or 5 or 6 or 7 just changes the max.

There is NO M4 4H listed.

I found a M4 4H on this calculator and it also shows min. pitch dia. 3.545 is correct. It represents the latter "H".
GewindetoleranzRechner ISO-Gewinde DIN 13

Sorry it's in German but plug in you numbers on the right side for internal threads (Innengewinde) and on the left for external threads (Aussengewinde).

Check again! On the M4 4H one side should be 3.545 and the other side should be bigger.

I don't know why anybody would want a M4 4H thread gage. Could be for Aero/Space. In that case - "MJ thread" see here for MJ 4x.7 4H6H :http://mdmetric.com/tech/thddat23.htm

 

[yanshi]

I am very sure 4H and 6H don't have the same limit sizes.
M4x0.7 6H Minor diameter D1 (3.242-3.422) Pitch diameter D2(3.545-3.663) Major diameter D(4.000-4.219)

All these data from Machinery handbook http://www.gaugestools.com/wp-content/uploads/2017/10/Machinery´sHandbook.pdf

 

[Gordon B. Clarke]

We're cutting an M4 x .7 metric thread. Print calls for a 6H thread classification. Our normal procedure is to just order a thread gage of the proper classification and check our thread with it. However, we have a 6H gage and a 4H gage and they both have the same size go and no-go pitch diameters stamped on the handle. why would a 4H and 6H have the same limit sizes?

Water under the bridge now but it'd be nice to see a photo of what actually is stamped on the thread handles.

Standard M4 has a 0.7 pitch and the tolerances are external 6g and internal 6H.

Simply by writing M4 all tolerances are given. For another pitch and/or tolerance then that must be stated.