$2 Router Table Clamps

This project is cheap fun assuming you have available scrap or scrounging skills.
The original idea was spotted on Thingiverse,  here's the link:
https://www.thingiverse.com/thing:776 

Materials used:
1/2" birch plywood https://www.menards.com/main/building-materials/panel-products/specialty-panels/hardwood-panels/1-2-x-20-23-x-20-23-c2-russian-birch-plywood/1254000/p-1452209920854.htm

3/4" hardwood dowel (to make the pivots)
1/4-20 threaded rod
1/4-20 nuts
1/8" hardwood plywood (to make the nut retainers)
1/8" HDPE sheet (to make the plastic washers)
A scrap piece of birch flooring (to make the knobs)
Woodglue

The knob in the centre of this image has a 1/4-20 nut embedded just slightly deeper than flush. The recess for the nut is a hexagon pocket cut with a 1/8" diameter bit which leaves a bit of material where there should 6 sharp corners, this provides a nice interference fit.  Barely visible leaning against the knob is a wooden washer,  this will be glued to the knob to act as a nut retainer.  To the right of the knob is a threaded rod and an "E-Z LOK" threaded insert.  The inserts have been installed from the underside of the table surface.  Every hole seen in the table above has a threaded insert installed.

 An exploded view.  The wooden washer is glued to the knob to act as a nut retainer.  In practice the nut may fit tight enough in the knob to make the retainer unnecessary.  If the knob is hardwood (I used birch hardwood) the knob itself could be tapped for threads eliminating the nut.  The pivot has been milled to provide a flat surface, this increases the holding power of the knob assembly.

WARNING: These clamps will collide with the router if you get too close.  For added clearance a bolt can replace the threaded rod and knob.