14''-20 x 1'' PhillipsSlotted Round Head Machine Screw

Designed for maximum grip under load application, these Hi-Grip screwdrivers have a slotted tip, round blade and a flared flat head

Name, Pan Head Screw ; Material, Alloy Steel ; Thread, Metric thread ; Head shape, Button head ; Drive Type, Slotted or Phillips

slot barat screw, consisting of a single slot at the head of the screw Generally not Flat head screwdrivers and driver bits

slot machine starburst It's called a spanner slotted head Useful site here Hard to find in the UK, why the owner used one I cannot imagine