Alloy plates were optional 'race parts' usually. At least in the T/X/Z
parts list shows 2 driven plates. 4 of 1 type and 1 of another. (total 5)
Yeah just checked
you probably have this which is aluminium
Part # = 21451-40001
Part Description = PLATE,CLUTCH DRIVEN
Model Count = 26
PE250B 1977 246 PE250 DUAL PURPOSE
PE250C 1978 246 PE250 DUAL PURPOSE
PE250N 1979 246 PE250 DUAL PURPOSE
PE250T 1980 246 PE250 DUAL PURPOSE
PE250X 1981 246 PE250 DUAL PURPOSE
RM250A 1976 246 RM250 OFF ROAD
RM250B 1977 246 RM250 OFF ROAD
RM250C 1978 246 RM250 OFF ROAD
RM250C2 1978 1/2 246 RM250 OFF ROAD
RM250D 1983 246 RM250 OFF ROAD
RM250E 1984 246 RM250 OFF ROAD
RM250F 1985 246 RM250 OFF ROAD
RM250G 1986 246 RM250 OFF ROAD
RM250H 1987 246 RM250 OFF ROAD
RM250J 1988 246 RM250 OFF ROAD
RM250-N 1979 246 RM250 OFF ROAD
RM250-T 1980 246 RM250 OFF ROAD
RM250-X 1981 246 RM250 OFF ROAD
RM250Z 1982 246 RM250 OFF ROAD
RM370A 1976 372 RM370 OFF ROAD
RM370B 1977 372 RM370 OFF ROAD
RM400C 1978 402 RM400 OFF ROAD
RM400N 1979 417 RM400 OFF ROAD
RM400T 1980 417 RM400 OFF ROAD
RS250T 1980 250 RS250 DUAL SPORT
RS250X 1981 250 RS250 DUAL SPORT
Alpha says 4 of those are std but my printed parts book says the qty 4 plates is this
Part # = 21451-40000
Part Description = PLATE,CLUTCH DRIVEN
Model Count = 6
PE250B 1977 246 PE250 DUAL PURPOSE
RM250A 1976 246 RM250 OFF ROAD
RM250B 1977 246 RM250 OFF ROAD
RM250C 1978 246 RM250 OFF ROAD
RM370A 1976 372 RM370 OFF ROAD
RM370B 1977 372 RM370 OFF ROAD
If you did happen to want Alloy plates, Barnett do them but they are 'cryodized' and ment to be a lot better than the plain OEM alloy plates. Lighter weight but more durable.