This larger base works with the Ellipse/Circle Router Jig for more design flexibility and ellipses with narrower proportions. The larger size increases the maximum difference between the major and minor axes from 8" to 14". In other words, the maximum length of the major axis remains 52", but the minor axis can be up to 14" shorter than with the standard base.Base includes 2 extra dovetail keys with pivot pins.Made of solid phenolic for easy sliding.