Rockler - Universal Fence Clamps (Rating: 5)

Well you could get by without them.

$15 a pair from Rockler.

What the heck are they?

They hold aux. fences and stopblocks to your existing rip fence, for crosscutting and dado operations where the blade would otherwise obliterate your existing fence.

Just rip a piece of ply, melamine, or other stable stock, drill two holes for the clamps, and clamp away.

The biesemeyer aux. fences with clamps are around $150. The only advantage I see is that their fence is exactly 1" thick, allowing for easy math. I will just use a tape.

Get a pair.