I have the Aa size on my S7.
The standard A size tool holder will not go low enough, BUT the genuine Multifix made some special A size tool holders for the Myford 7 lathes and I think the set was designated Am.
Nick.
Edit:- Even when using the Aa size with insert tooling, the 8mm square shank tools only just go low enough, to be on centre height (I use 10mm square, milled down to 8mm high, leaving them 10mm wide).
Edited By Nick Hughes on 13/03/2020 00:07:28