Self Tapping Screws

Recommended hole and drill sizes for Type AB and B self tapping screws - in thermo (pliable) palstics

Note: because of the vast differences in these plastics, the following table is only intended as a guideline. It may be necessary to increase or decrease the recommended hole size to obtain optimum fastening conditions.

Catalogue pages:	74. Self Drilling Screws	75. Self Drilling Screws Type 17	76. Washer /Seals
76. Chip/Drywall Screws	77. Drywall Screws	77. Collated Drywall Screws	78. Screws
79. Gutterbolts	80. Machine Screws	81. Machine Screws	82. Machine Screws
83. Machine Screws	84. Self Tapping Screws	85. Self Tapping Screws	86. Self Tapping Screws
87. Self Tapping Screws	88. Self Tapping Screws	89. Self Tapping Screws	90. Self Tapping Screws
91. Self Tapping Screws	92. Self Tapping Screws	93. Self Tapping Screws	94. Self Tapping Screws
95. Self Tapping Screws	96. Woodcrews - Twinfast	97. Woodcrews - Surefix	98. Woodcrews - Surefix
99. Woodcrews	100. 101. 102. Washers	108. Screwdriver Bits
Pdfs:	74. Self Drilling Screws	77. Drywall Screws	78. Screws
79. Gutter Bolts	80-83. Machine Screws	84. Self Tapping Screws	96 - 99. Woodcrews

Type 'AB'

• Firstly make a hole to suit the diameter of the screw being used. The hole can be clean punched or drilled as shown above in Fig 1 or plunged as shown in Fig 2.

Type 'B'

• Fig 5 for light sheet assembly, no clearance hole is necessary in the top sheet.
• Fig 6 and 7 When fastening to solid section of casting or die-casting, or to heavy guage sheet metal, a clearance hole in the top sheet is required. If a clearance hole is not provided, the total thickness of material must be taken into account when deciding on the tapping hole size. Remember that the thickness of material increases, it becomes more difficult to pull the two sheets together tightly.

Recommended Hole and Drill Sizes

Type B self tapping screws (Drilled or cored holes) in non ferrous castings, aluminium, zinc, brass, bronze etc.

Notes:

1. Cored holes. A side taper of 1°11' is permissible. The diameter of a cored hole should equal the nominal hole size shown in the table to the right at one half the screw penetration depth.
2. Porous castings may require the use of a smaller hole and/or increased depth of engagement.

 

Type AB, B Self-Tapping Screws

18-8 Stainless Steel, mild steel, monel metal, brass and aluminium alloy sheet

Notes:

1. Because conditions differ widely it may be necessary to vary the hole size to suit a particular application.
2. 18-8 quality stainless steel self-tapping screws are much softer than case hardened steel screws and therefore case must be exercised in using them. They cannot be used in very hard material. Also due to the galling tendency of stainless steel they should not be used in stainless steel sheet

 

Ullrich Aluminium Company Ltd, New Zealand

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