Precision Products & Performance Center produces these solid flat tappet lifters. They are high end, but Charlie says they are necessary if you expect your lifters to live in a very high rpm application with an aggressive camshaft. The tool steel lifters are exceptionally hard, and PPPC holds the outside diameter to extremely tight tolerances to reduce the chances of sticking a lifter. They are also rebuildable, which includes regrinding and polishing the tappets, which makes the lifters more affordable if you reuse them after a rebuild. Finally, notice the pressurized oiling hole in the tappet face which injects oil between the lifter and the cam lobe to prevent lobe wear.