John
Doug Galbreath's web site is:
[email protected]
click on his Free Flight Stiff.
This head will only accept the nelson plug which he sells. Nelson plugs have a special thread size, therefore reg plugs will not fit. The plugs are very durable & do not blow as easy as the Cox plugs.
These plugs will accept 65% nitro. I am not going to state rpm ratings, since engine set ups can differ. You will however notice a large increase with the Nelson plug.
Gene