The pressure gauge comes with a threaded male insertion that will fit only OMER pneumatic spearguns. It simply just screws into the back of the gun to measure the pressure.
The adapters are needed to use the gauge on other brands of spearguns. You will need the gauge and the adapter to use this gauge on other brand spearguns like Cressi-sub, Mares, Seac, etc. The adapters are sold separately. Thanks to the adapters, you can fill a variety of pneumatic spearguns.
