Good luck sorting it all out and happy hunting amongst the early flatgates. Ruger has never kept detailed records down to the finer points for each and every gun produced and they are well known for finding older parts and using them up or making clean-up guns sometimes years later so with Ruger you can never say never about anything. The above are general characteristics and doesn't mean some parts were used up in later guns or parts got swapped out or some other oddity didn't happen. Type 2 flatgate has a serrated front sight and a short throw ejector rod housing. Type 1 flatgate has a non-serrated front sight and no hyphen between the words Single and Six on the frame in serial numbers below 1986. Type 4 flatgate has all the same characteristics of the Type 3 except the ER button is the large round button with a concave face. Others may come along with better info but this may help. Type 3 flatgate has serrated front sight, long throw ERH and small serrated ER button. A hypen would be present between Single and Six on the frame. Others may come along with better info but this may help. Below info gleaned from the RENE reference. Not an expert or collector but will try to answer your question since no one else has yet chimed in.
