RE: You should be able to locate some BA screws in Canada

Unlike Aus & NZ, we in Canada have never used BA screws. It was always Imperial (SAE NC, NF & NS) until the powers that be switched us over to the metric system when I was a kid.

Re: I've mounted many a one piece Parker Hale base to the various model SMLE 303 rifles and the screws are normally No 4BA for receiver and No 6BA for the rear bridge. I have the BA set of taps (Nos 1 to 6) and plenty of the screws. The PH mounting system was poor although it was about all we could get for years before the Weaver system became available in NZ. The cone shape recoil stud protruding from the base of one ring into a corresponding recess in the one piece base was a piece of poor engineering as the cone and recess taper worked to lift the ring under recoil so needed the ring to be kept very tightly clamped to the base. Problem was the long star headed through bolt doing the clamping was soft and easily snapped if torqued too tight. As soon as the Weaver system became available to me I ditched PH and never fitted another.

Thank you for the sizing information. I have a bag of 100 6BA screws coming. Guess I'll have to locate a hundred 4BA to go with them!