Brian- as to transmission families- 1000, 2000, 2100, 2200, 2500 are all the small World. MD3060, MD3560, 3000HS, 3000RDS, 3000MH, 3000TRV, 3200TRV, 3500HS, 3500RDS, B300, B400 are the middle sized World. HD4060, HD4560, 4000HS, 4000RDS, 4000MH, 4000TRV, 4500HS, 4500RDS, 4700RDS (7speed-6speed with deep first), B500 are the large size World. Just being picky. Good Luck, TomC