These are a bayonet type 1/4-turn twist lock cap. Fits all U.S. manufactured deep-cycle batteries except the (so-called) "maintenance free" type, or those with the plug-in 3-cap bars, such as the West Marine Sea Volt or the Interstate 12 volt group 27 marine.
Flip-top battery vent cap, 1 1/8" bottom insert width, total width 1 3/8" x 1/4" height into battery insert and 1" height above the battery insert. Water Misers are molded plastic "flip-top" vent caps designed to reduce and ease maintenance on flooded Lead-Acid batteries. There is no need to remove the caps when charging, filling, or equalizing the batteries. When charging, the plastic pellets capture up to 90% of the moisture and acid droplets. This reduces acid fumes, corrosion, and keeping the battery tops much cleaner and dryer. Excess water is dropped back into the battery cell. Water loss is reduced, which extends time between watering.
We no longer carry the Hydrocaps, due to excessively long lead times and poor delivery.