Rochester Gauges Model 8640 Spiral Gauge.  Tank depth should be at least 1/2” greater than the length of the gauge.   The additional depth may be considered "reserve" at the bottom of the tank that will not be measured.  
- Designed for top mount
 
- 1-1/2” MNPT tank connection
 
- TwinSite Sender Dial 240-30 Ohms or 0-90 Ohms
 
- Suitable for up to 25 psig maximum
 
This product is not always in stock so please contact us if you need it immediately.