[Ford blue blood]

Those were used in Hi Performance solid lifter cam engines, 427 specificly, others I feel as well. Shims to establish correct spring heigth/tension were inserted under the cups. They were required when putting the 427 tripple springs on Boss 302 heads...so if your cam/lifters/springs are for a 406 Hi-Po then yes. Having said that be sure to check for spring bind at max lift.