These Viton seals fit over the standard 0.50″ diameter valve guide. Outside diameter is 0.550″ when installed. Fits inside all single and most dual valve springs. Fits inside Good Parts dual valve spring sets. Good Parts valve spring seats are recommended to keep valve springs centered around the guide when using dual valve springs with valve seals. Requires 0.165″ clearance between guide and retainer at full lift. This set includes 12 seals and an installation tool.