you'd have to find where you read that and figure out what they mean, all thermostats are "double acting" in that they open above a certain temp and close below that temp, there is nothing different about one for a 261

Bill


Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics