Originally Posted by
jeebusaurousrex
Park Tools BBT-18 has the correct number of splines but is way too big.
The BBT-18 is for externally notched bottom brackets, such as XTR, Bontrager and Truvativ.
Yours is not a Suntour Sprint, though you have probably already worked this much out. I think I've seen such a cup in the past, though I can't recall what tool is needed. Does the fixed cup have the same fitting?