Joint Set are NOT usable alone.  

There are three different ring widths; 5mm, 8mm and 12mm available for the Flat Ring Set. Each basic set includes a part we call "joint" which sets the ring thickness to 2.0mm. Additional three thickness(1.5mm/2.5mm/3.0mm) are available by using separately sold Joint Sets.

They must be used with a 8 mm size 25 flat set.  PMC123 no longer has the set needed to work with this joint set.  It is still made and can be purchased from other suppliers. 

Ring Maker conversion Chart

Small  will make rings from size 4 ½ to 6 after firing (Japanese size 17)

Medium  will make rings from size 6 to 7 ½ after firing (Japanese size 21)

Large  will make rings from size 7 ¾ to 9 after firing (Japanese size 25)

Xtra Large  will make rings from size 9 ¼ to 10 ½ after firing (Japanese size 29)

 These are being closed out, hurry while supplies last!