Compression Tester / Pack Size:1Foley/PLP 186-056, Rotary 9036, Prime Line 7-05951, ESF 186-056, Foley/Belsaw 5978889, Quality 480617, Oregon 42-422, JThomas T-311, Bailey's G 320HD, Laser 97384, NHC 399-5161, Napa 7-05951, Ratio Parts 800-052, EG/F1 9206889 3/4" hex at base for installation and removal, 2 3/4" diameter, Reads up to 200 PSI, Fits 14mm and 18mm spark plug holes