(a) a first L-shaped member having a first arm including a linear edge engageable with the generally planar surface and a second generally planar arm defining a first axis substantially perpendicular to said linear edge;

(b) a second L-shaped member having a first arm including a linear edge engageable with the generally planar surface and a second generally planar arm defining a second axis substantially perpendicular to said linear edge of said second L-shaped member first arm; and

(c) means for mating said first and second L-shaped members to each other with said first and second axes superimposed one upon the other for relative pivoting movement of said L-shaped members with respect to said superimposed axes, and with said linear edges diverging from said superimposed axes at a common point therealong;

(d) wherein each of said second arms defines a fin on a side of said superimposed axes opposite a corresponding first arm, said fins jointly forming a channel within which the workpiece is received substantially perpendicular to the generally planar surface.