Accuracy notation STD is the accuracy of the tap recommended when machining thread accuracy class 2 or 6H internal thread equivalent. The accuracy notation STD indicates how much tolerance the pitch diameter of the tap is controlled. It is an abbreviation for Standard. STD+1, STD+2, etc. are called oversizes.

As the number of STD+1, STD+2, and so on increases, the tolerance position of the tap pitch diameter increases. How large the tolerance position varies depending on the type of tap and the pitch. For cutting taps, it is +20 μm for every STD+1 at a pitch greater than or equal to 0.7. The pitch is +15 μm with a pitch of 0.6 or less. For rolled taps, it is +12.7 μm for every STD+1, regardless of pitch.

The tap accuracy STD is set so that it is easy to aim for passing the thread accuracy class 2 and 6H class for each application and size, such as taps for general use and taps for SUS. Therefore, even with the same thread size, the tap accuracy may vary depending on the type of tap.

(1) Pitch diameter (2) Basic pitch  diameter (3) JIS tap Limits (4) OH Limits(5) Previous JIS internal thread  (6) JIS internal thread

・ Cutting tap accuracy OH accuracy8015-2.pdf

・ Rolling tap accuracy RH accuracy8015-3.pdf

・ Is there a tap that can be processed with a thread accuracy of 6H? 

name			Screw Grade (Tolerance Range Class)
Thread type	division
Metric Thread (M)	external thread	JIS	4h	6ｇ	8g
		ISO
	internal thread	JIS	4H、5H	5H、6H	7H
		ISO
Unified Screw (U)	external thread	JIS	3A	2A		1A
		ISO
	internal thread	JIS	3B	2B		1B
		ISO
Whitworth screw (W)				Class 2	Class 3	Class 4
Purpose			Screws that require a tight fit	For tightening general machines	General Machinery Chore Screws	Black Skin Bolt