The CTA Manufacturing 3", 4", and 6" Piston Ring Compressors, Nos. 4021, 4023, and 4024, features a ratchet mechanism with square drive tools to adjust diameter, an enlarged crimped edge to prevent compressor from entering cylinder, and a spring steel construction with a double band design. The 4021 is for passenger cars. It has a depth of 3" and a range of 60 - 175mm. The 4023 is for cars and light trucks. It has a 4" depth and 60 - 175mm range. The 4024 is for tractors and diesel trucks. It has a depth of 6" and a range of 60 - 175mm.