Grr-Ripper Thumb Knobs
Whilst this is a spare part for the Micro Jig GRR-Ripper, they can also be used with Micro Jig T-Bolts (GRH-12-K) which fit into Torquata or Incra T-Track.
Sold as a packet of 4, the knobs measures 28 x 13.5 x 19mm. Thread size is 1/4-20 (1/4" 20 TPI).