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.

• semi-rigid transparent protective tube
• 5.25" high and 3" in diameter
• sealed with water resistant polypropylene plugs
• may be opened from either end
• it floats
• weighs less than 2 ounces
• much less weight and space in your gear bag than the "other case"