This case was designed especially for the ANALOX EII CO CARBON MONOXIDE SCUBA TANK TESTER and the ANALOX O2EII SCUBA TANK NITROX TESTER which are identical in size. That's not to say that you won't find it convenient for many other products of similar size.
Turtle-Tube Analox model protective case
The Analox O2EII is shown here in the Turtle-Tube, the protective gauge case made by Sea Turtle Scuba, Inc. It also fits the ANALOX EII CO CARBON MONOXIDE SCUBA TANK TESTER
This case will protect your tester from damage even if you just toss it into your gear bag with the rest of your gear.