Centre Drill A4 DIN 333 Form A

HSS centre drill, form A, 4 mm pilot on a 10 mm body.

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Specifications

Size designation	A4
Pilot diameter	4 mm
Body diameter	10 mm
Overall length	63 mm
Pilot length	3.7 mm
Countersink angle	60°
Material	HSS
Standard	DIN 333 form A

Description

A form A centre drill to DIN 333, used to start an accurate hole and to cut the 60° centre that a lathe tailstock or a between-centres grinding operation locates on. The short stiff pilot resists the wandering that a long jobber drill suffers on an unprepared face, which is why centre drilling first is standard practice before any deep hole. Form A has a plain 60° countersink; form B adds a protecting 120° chamfer.