COMP Cams 850-1 Hydraulic Roller Lifter for Small Block Chevy 305/350 with OE Hydraulic Roller Camshaft 0.842 inches diameter; 122 gram weight; 2.66 inches seat height Performance replacement for stock hydraulic roller lifters or retro-fit hydraulic roller lifters for non-roller blocks Decrease friction and increase longevity when directly compared to flat tappet lifters Accept much more aggressive cam profiles than flat tappet lifters will allow