The integral washer recess is to accommodate a resilient watertight sealing washer. The washer surface provides bearing surface to the drive socket. Available in 1/4”(8G), 5/16”(10 or 12G) and 3/8”(14G) socket sizes.
Coarse threads normally used for all timber applications and for steel for the lesser thicknesses (1mm- 5mm normally).
Common screw examples include; 10g-16TPI, 12g-14TPI and 14g-10TPI.
Fine threads are for use with thicker steels (2mm-12mm thickness).Common screw examples include; 10g-24TPI, 12g-24TPI and 14g-20TPI.
Hi-Tens or 50 series self drillers are for much thicker steels and have a longer drill tip and fine thread.
We stock 8gx12, 10g x 16 to 25, 12g x 20 to 55, 14g x 22 to 150.