Three inch single-groove hydraulic piston. 

Fits the following Ford tractors: 1800 Series, 2000 Series 4 Cyl 62-64, 2030 Compact Tractor, 4000 Series 4 Cyl 62-64, 4030 4 Cyl 61-62, 4040, 4120, 4130 4 Cyl 63-64, 4140, 501 Series, 600, 601, 601 Series, 650, 701 Series, 800, 801 Series

Also fits Ford 2000 3 cylinder, 3000 and 4000 3 cylinder series tractors only when they require a 3" piston (if you have this model of tractor, measure your piston before ordering as different sizes were used). 

Massey TO35 (s/n 179304 & up), MF35, MF50, MF65.

For early production tractors: MF135, MF150, MF165 using 3" dia. piston. This is an update to the original style piston with three grooves and three metal rings.