No. 12, Solid Brass, Countersink/ Countersunk (csk), Slotted Head, Wood Screws. Fixaball.co.uk, sells all lengths of No. 12 (5.5mm) brass, slot, csk wood screws at the best internet prices, with free, first class post.. Orders placed before 2pm are usually dispatched same day (Mon-Fri).. Please make your size and pack quantity selection from the drop down menus.