P251 (Oil Filled) with crimp casing models are designed for corrosive environment which media do not corrode the brass and which do not have high viscosity or do not crystallize. Glycerin is filled to protect gauge againt system or equipment where pulsating pressure or mechanical shock and vibration are apparent. It is suitable for compressor, hydraulic, pneumatic, filters, pressure regulators and etc. 

Dial Display: 2.5" 
Connection: 1/4" Male NPT 
Mount: Bottom 
Case: Stainless steel 304 
Window: Polycarbonate plastic 
Element Tube: Lead-free brass (≤0.25%) 
Connection: Lead-free brass (≤0.25%) Accuracy: ±1.6% of range 
Pressure range: Dual scale
Blow Protection: Top, Rubber 
Ambient temperature:-4 to 140 °F 
Process: Maximum 140 °F 
Do not use for oxygen service

Resources

Technical Datasheet for Unijin P251 Pressure Gauge