A7304-4 can be used to retrofit B1559 series steel liquid level gages to include the shut-off feature.  Each gage requires 2 of the A7304-4 shut-off sub-assembly.  In addition to the o-rings supplied with the original gage, the following must also be ordered:

A2699-27  Qty. 2  For use at the mounting thread
A2699-4    Qty. 2  For use around the adjustment stem

This sub-assembly is not compatible with gages manufactured prior to 2017.