This versatile sub base is pre-drilled to fit Sears, DeWalt 625/621, Makita,
Hitachi, Freud FT2000E, Ryobi, & Elu 177 routers. The 1.2" center opening is rabbeted to accommodate the mounting flange of Porter-Cable-style universal template guides. It's a good way to enable your router to use template guides without totally obscuring the work; the 11/32" plastic base plate is clear as glass, so (depending on your router's base design) you'll be able to see dovetail jig guide fingers and other templates through the base rather than putting yourself in harm's way for a look underneath the machine.
The Offset model is teardrop-shaped and measures 12" in length with a large 1-3/4" diameter knob located 7-1/2" from the center hole of the jig.