My dividing head is a Yuasa/News 6" with a nice Buck chuck on it that I snagged on Ebay. 

Unfortunately it only came with 1 plate, the 15 - 20 'A' plate which doesn't include a factor of 7.  I gambled and purchased a set of plates used on the ubiquitous import 6" rotary tables- the mounting is similar but unfortunately the hole is too large and the screw holes don't match up.  Here the plate is set up so I can reduce its thickness out to just past the screw holes.  Then I'll fit a plug and put in the right holes to fit my head. 

In roughing the plug, I tried pushing the lathe a bit. I have a short length of 3" mild steel- I don't know the alloy but it cuts sort of like 1043/1045. I set up a .350" DOC with minimum feed, it loaded the lathe significantly and I could see the toolpost flex but it finished the cut just fine, no chatter and left a moderate finish. The chips were wide, thin and stiff, came off slighly straw colored and broke nicely. The cut was hot and needed a lot of cutting oil, and overheated the HSS bit. The head was set in the middle of the 8 speeds- I really need to set up a tach. As I worked the plug down to the right dimensions, I found a .080 DOC with a higher feed & RPM worked better, not as dramatic but it left a better finish and wasn't as scary.

This is one of the new dividing plates, just over 4" OD.

This is a closeup of the plate I adapted.  The brass screws are a little bizarre...  First I fit the plug, put screws in the three holes and soldered everything.  Then I turned off the protruding screw heads and set up the new holes.

And lastly I turned the backside of the plate to match its thickness to the original plate.

;;; eof