Thanks for the reply, I had realised they were for making holes for screw, hence the countersink, it was just the taper that confused me, as the threads and core of a screw are not tapered (just the tip) I don't see the need to taper a hole.
fair enough, I hadn't realised that.
As you can see from the photos, we have a large selection of screws; some of which are obsolete. From my experience, I can tell you that old wood screws were parallel. When I started my apprenticeship in 1956, I was taught that you were allowed to knock the screw in the length of the plain bit of the shank as, with the crews being parallel, it made a hole the right size for the plain bit of the shank. Also, if you measure across the slot of the screw in 16ths of an inch and multiply it by 2 and then subtract 2 it gave you the gauge of the screw. I am now 81 years of age and still go to work every day; I must be mad!
And had slotted heads.
The slots are for taking them out. After using a Birmingham screwdriver to put 'em in
