①,1. Where specifying nominal size in decimals, zeros preceding the decimal shall be omitted. 2. The maximum permissible variation in the number of threads per inch shall be plus or minus 10 per cent of that which is tabulated for the respective screw size. 3. Cut thread type screws are usually supplied with single lead threads for all screw lengths. 4. Rolled thread type screws may be supplied with either single lead or double lead threads at the option of the manufacturer, however, single lead threads are preferred where the nominal length of the screw is shorter than 4 times the basic screw diameter. Points shall be sharp, however, no extrusion of excess material beyond the apex of point resulting from thread rolling shall be permissible. For additional requirements refer to General Data. ②,Cut Thread Screws. The length of the thread on wood screws having cut threads shall be equivalent to approximately two-thirds of the nominal length of the screw. ③,Rolled Thread Screws. Rolled thread wood screws shall have a length of thread equivalent to at least four times the basic screw diameter or two-thirds of the nominal screw length, whichever is greater. Screws of nominal lengths which are too short to accommodate the minimum thread length shalJ have threads extending as close to the underside of the head as practicable. |