For BSB 1/4 Taps and Dies the closest available in our range is 1/4 BSF x 26 TPI Thread Form; both standards are the same outside diameter and flank angle (55 deg). The main difference is that the minimum core diameter of BSF is 0.02mm less than the BSB thread form depending on which authority you choose to cite. In practical terms it may mean that when screwing a 1/4 BSB female brass fitting onto a threaded 1/4 BSF spigot there may be some looseness which can to taken up by the use of thread sealing compound or PTFE tape.
