I stepped from the slimline to the Flat top American Double Twist. Not too hard to make. Just remember that the tenon gets taken all the way down to the brass, and don't leave the upper end of the lower barrel proud. (Turn it a wee smidge thin if you have any doubt, otherwise the pen won't twist. D.A.M.H.I.K.T.!) Assembly is a bit tricky the first time, as the kit is engineered with very little wiggle room. You need to sand on the brass, and file out the inside just a bit to make things work smoothly. In the end, you come out with a really nice looking pen. It is my favorite style to carry and write with.
I also am turning 7mm Europeans, but the tenon there is a bit touchy. I have had to glue some center rings on with thick epoxy, and shim them a bit. Also a nice looking pen, but not quite as formal as the flat top in my opinion.
I also agree that you never really master the slimline. I have turned stepped versions with all kinds of shapes, and made my own center rings from contrasting woods and acrylics. I have gone through about 40 of them, and I am still coming up with new ways to do them.
Everybody I know, and most of their friends have a couple of pens now. My girlfriend's sisters should be able to lose them about as fast as I turn them, so I don't worry about getting buried alive under mountains of pens. [
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