Does anyone know, can I use a gas fuel pressure tester to connect to and test a Cummins diesel?

Specifically I'm wanting to check my lift pump preaasure after the filter by connecting to the schrader valve.

I know the testor specifically says not for diesel but I cant understand why

Thanks in advance

Lift pump pressure should be well within the range of a gasser, I'd try it...

Lift pump is 15-20, I was wondering if there is a reason the gas gage would'nt work, or break down (mybe different seals or provide a false pressure). Or is this simply a safety to keep some one from hooking up after the high pressure injector pump and blowing the gage face off?

It's not the seals...Probably liability

I have used an old air conditioning gauge set.