Most suppliers just sell 1/4 BSF stuff as BSF/bsc, nuts, bolts etc.
1/4 screws or bolts BSF or bsc will fit 1/4 BSF helicoils no problem.

Same with ww/UNC in smaller sizes.

Personally if i was helicoiling a primary case i'd use UNC or M6 you can
buy them anywhere and they are much cheaper, as are the bolts etc.