The Astro Pneumatic 78817 3 piece Two Way Extension Set including the following extension sizes - 3/8", 1/2" & 1/4". This unit has a Dual function design allows the two way extension to be used as a Standard Extension or as a 360° Swivel Universal Extension. The outer diameter of each extension is: Ø23mm for 3/8" Extension, Ø29.05mm for 1/2" Extension and Ø17.9 for 1/4" Extension. The vverall length of each extension is: 78.23mm for 3/8" Extension, 94.32mm for 1/2" Extension and 56.7mm for 1/4" Extension.