This tool is used to check piston to head clearance on EMD power assemblies. 1/8" wire is inserted into both sides of the holder and the assembly is placed on the top of the piston. The engine is barred over and the wire removed to measure the compressed wire dimension per OEM instructions. Equivalent to EMD # 8243220
1/8" lead wire is also available in a 5 Lb spool - T68310 (8243661)