Dzus self ejecting quick release fasteners are designed for use on curved or contoured surfaces where ejection of the fastener is essential to remove the top panel. The ejecting mechanism also gives an instant signal that the fastener is unlocked. This Dzus Fastener has a flush head and is made of zinc plated mild steel.Flush head for improved aerodynamicsQuick release, simple 1/4 turn to attach or removeSelf ejecting, ideal for fastening curved or contoured panelsDzus self ejecting fasteners are available in 2 different body sizes:EHF5-XX has a 37mm head with 27mm between the rivet holes, is 1.47" long, 7/8" wide and requires S5 attachment springs (sold separately in a range of clearance options)EHF6-XX has a 44mm head with 34mm between the rivet holes, is 1.725" long, 1 3/32" wide and requires S6 attachment springs (sold separately in a range of clearance options)To calculate the correct pairing of fastener and spring use the following formula:Add together the thicknesses of both pan