Been a while since I bought the blanking caps from Steve but have only just tried fitting them. Only one seems to fit. Have measured the inside diameter and the one that fits is 12.5mm and the three that don't are 12mm. Measured one of the outlet pipes and it is 12.3mm. The one that fits doesn't slide all the way down and seems to be slightly tapered internally. Looks like some fettling is required.... hey ho.
FZS 1000 Gen1 (2003)
Tiger 900 GT Pro (2020)
Tiger 900 GT Pro (2020)