Synsphyronus callus is a species of pseudoscorpion in the Garypidae family. It is endemic to Australia. It was described in 1947 by American arachnologist Clarence Clayton Hoff.
The body length of the holotype female is 3.3 mm. The colour is brown.
The species occurs in south-west Western Australia in rocky coastal habitats. The type locality is Rottnest Island, with a paratype specimen obtained at Cottesloe Beach near Perth.
The pseudoscorpions are terrestrial predators.