Amazon.com: Alemite 42030-A Button Head Coupler, Standard Pull-On Type, For Use with Standard or Giant Button Head Fittings, 1/8" Female NPTF : Automotive
WESTWARD, For Use With 5/8 in Button Head Grease Fittings, Button Head Coupler 5/8" - 3APG4|3APG4 - Grainger
STANDARD BUTTON HEAD COUPLER 5/8" (ACCESSORY)- - Macnaught