A tap cuts a thread on the inside surface of a hole, creating a female surface which functions like a nut. The three taps in the image illustrate the basic types commonly used by most machinists.

 

Order No	Size (mm)	Over length (mm)	Flute Length (mm)
TAPS-11701	1/4-20 UNC	80	17
TAPS-11702	5/16-18 UNC	90	20
TAPS-11703	3/8-16 UNC	100	22
TAPS-11704	7/16-14 UNC	100	22
TAPS-11705	1/2-13 UNC	110	24
TAPS-11706	9/16-12 UNC	110	26
TAPS-11707	5/8-11 UNC	110	27
TAPS-11708	3/4-10 UNC	125	30
TAPS-11709	7/8-9 UNC	140	32
TAPS-11710	1-8 UNC	160	36
TAPS-11711	1-1/8-7 UNC	180	40
TAPS-11712	1-1/4-7 UNC	180	40
TAPS-11713	1-3/8-6 UNC	200	50
TAPS-11714	1-1/2-6 UNC	200	50