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Applicable to screw types as indicated by code symbols.
  • Type AB thread forming.
  • Types B and BP thread forming and Types BF and BT thread cutting.
  • Type C thread forming and Types D, F, G, and T thread cutting.
This type of recess has a large center opening, tapered wings, and blunt bottom, with all edges relieved or rounded.
Unit of Measure

Manufacturer

Manufacturer

 N/A Industrial Fasteners Institute

Specifications

Product

 N/A Tapping Screws

Unit of Measure

 N/A English

Type

 N/A Type I

Nominal Size or Basic Screw Dia.

 N/A 1/4 in

Nominal Size or Basic Screw Dia. (Decimal)

 N/A 0.2500 in
Applicable to Screw Types1 N/A 1
3
4

Max. Head Dia. (A)

 N/A 0.492 in

Min. Head Dia. (A)

 N/A 0.473 in

Max. Head Height (H)

 N/A 0.175 in

Min. Head Height (H)

 N/A 0.162 in

Min. Head Radius (R)

 N/A 0.035 in

Ref. Recess Dia. (M)

 N/A 0.274 in

Ref. Recess Depth (T)

 N/A 0.148 in

Ref. Recess Width (N)

 N/A 0.036 in

Driver Size

 N/A 3

Max. Recess Penetration Gaging Depth

 N/A 0.144 in

Min. Recess Penetration Gaging Depth

 N/A 0.118 in

Codes and Standards

Codes and Standards

 N/A Abstract of ASME B18.6.4 1998
  • 1 1 = Circle, 2 = Diamond, 3 = Triangle, 4 = Square
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