JT chainwheel, see added picture for sizes as to fitment. Fits many models, hole of chainwheel 165mm.
According to JT fits amongst others:
KTM SX 1251984-1990
KTM EXC 125 1984-1990
KTM250 MX 1983 -1989
KTM 500MX 1988-1993
KTMLC4 6001988-1989
Chaintype 520.