Final answer:
The number of threads on iron pipe for propane manifold connectors on recreational vehicles depends on the standard used. Common sizes include 1/4-inch NPT and 3/8-inch NPT, both having 18 threads per inch.
Step-by-step explanation:
The number of threads on iron pipe that should be used on propane manifold connectors installed on recreational vehicles depends on the standard used for the connectors. The most commonly used standard for propane manifold connectors is the National Pipe Thread (NPT) standard. NPT connectors have tapered threads, and the number of threads per inch determines the size of the connector.
For propane manifold connectors, a common thread size is 1/4-inch NPT, which has 18 threads per inch. Another common size is 3/8-inch NPT, which has 18 threads per inch as well. These sizes are suitable for connecting iron pipes to propane manifold connectors on recreational vehicles.
It is important to ensure proper thread sealing techniques, such as using appropriate sealants or Teflon tape, to prevent any gas leaks when connecting the iron pipes to the propane manifold connectors.