Machinery's Handbook, 31st Edition
1834 SELF-THREADING SCREWS Flat Countersunk Head: The flat countersunk head has a flat top surface and a conical bearing surface with a head angle for one design of approximately 82 degrees and for another design of approximately 100 degrees. Because of its limited usage and in the inter est of curtailing product varieties, the 100-degree flat countersunk head is considered non-preferred. Oval Countersunk Head: The oval countersunk head has a rounded top surface and a conical bearing surface with a head angle of approximately 82 degrees. Flat and Oval Countersunk Trim Heads: Flat and oval countersunk trim heads are simi lar to the 82-degree flat and oval countersunk heads except that the size of head for a given size screw is one (large trim head) or two (small trim head) sizes smaller than the regular flat and oval countersunk head size. Oval countersunk trim heads have a definite radius where the curved top surface meets the conical bearing surface. Trim heads are furnished only in cross recessed types. Pan Head: The slotted pan head has a flat top surface rounded into cylindrical sides and a flat bearing surface. The recessed pan head has a rounded top and a flat bearing surface. This head type is now preferred to the round head. Fillister Head: The fillister head has a rounded top surface, cylindrical sides, and a flat bearing surface. Hex Head: The hex head has a flat or indented top surface, six flat sides, and a flat bear ing surface. Because the slotted hex head requires a secondary operation in manufacture which often results in burrs at the extremity of the slot that interfere with socket wrench engagement and the wrenching capability of the hex far exceeds that of the slot, it is not recommended for new designs. Hex Washer Head: The hex washer head has an indented top surface and six flat sides formed integrally with a flat washer that projects beyond the sides and provides a flat bear ing surface. Because the slotted hex washer head requires a secondary operation in manu facture, which often results in burrs at the extremity of the slot that often interferes with socket wrench engagement, and because the wrenching capability of the hex far exceeds that of the slot in the indented head, it is not recommended for new designs. Truss Head: The truss head has a low rounded top surface with a flat bearing surface, the diameter of which for a given screw size is larger than the diameter of the corresponding round head. In the interest of product simplification and recognizing that the truss head is an inherently weak design, it is not recommended for new designs. Method of Designation.— Tapping screws are designated by the following data in the sequence shown: Nominal size (number, fraction or decimal equivalent); threads per inch; nominal length (fraction or decimal equivalent); point type; product name, in - cluding head type and driving provision; material; and protective finish, if required. Examples: 1 ∕ 4 -14 × 1 1 ∕ 2 Type AB Slotted Pan Head Tapping Screw, Steel, Nickel Plated 6-32 × 3 ∕ 4 Type T, Type 1A Cross Recessed Pan Head Tapping Screw, Corrosion Resistant Steel 0.375-16 × 1.50 Type D, Washer Head Tapping Screw, Steel Metallic Drive Screws: Type U metallic drive screws are designated by the following data in the sequence shown: Nominal size (number, fraction, or decimal equivalent); nom inal length (fraction or decimal equivalent); product name, including head type; material; and protective finish, if required. Examples: 10 × 5 ∕ 16 Round Head Metallic Drive Screw, Steel 0.312 × 0.50 Round Head Metallic Drive Screw, Steel, Zinc Plated
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online