At the top of every valve stem sits one of the most highly stressed, lowest-cost assemblies in your engine: two little tapered wedges called keepers (or "locks") that grip the valve stem, held in place by a retainer that captures the top of the valve spring. This tiny cone-in-cone joint is what stops your valve from being ejected into the combustion chamber every time the spring tries to close it.

Here's the geometry: the retainer has a tapered internal bore, typically at a 7° or 10° included angle (measured from the centerline). The two half-moon keepers have a matching external taper and an internal profile with one, two, or three ribs that snap into machined grooves near the top of the valve stem. When the spring pushes up on the retainer, the taper wedges the keepers tighter against the stem — the harder the spring pulls, the harder the grip. It's a self-locking cone clutch.

Single-groove vs multi-groove: Multi-groove keepers (2 or 3 grooves) allow the valve to rotate slowly against the retainer because they don't lock rigidly — this is desirable for exhaust valves, spreading heat and wear evenly around the seat. Single-groove (or "bead lock") keepers grip rigidly and are used where rotation is undesirable, like on high-lift race engines running lash caps.

The 7° vs 10° debate: 10° is the traditional OEM standard — easier to install, self-releases when you compress the spring. 7° keepers grip harder and are preferred for high-RPM race applications where valve float and keeper walk-out become risks. But 7° keepers can also gall the retainer bore if reused, so racers replace them at freshening.

Real-world example: Chevy LS7 engines had a known issue where titanium valve retainers combined with high spring loads would let keepers "walk" or fret against the retainer bore, occasionally dropping a valve. GM's fix was to switch to tool-steel keepers with a hardened surface and add proper installation lubrication — cheap parts, expensive failure mode.

Rule of thumb for install: The gap between the two keeper halves should be roughly 0.030"–0.060" when installed. Zero gap means the keepers are bottoming on each other before gripping the stem — that's a dropped-valve waiting to happen. Too much gap means undersized keepers or a worn stem groove.

Every keeper carries the full spring seat load (often 150+ lbs static, 400+ lbs at max lift) times the valve events per mile — millions of cycles on a $2 part.