9/16x20tpi is a very common size .
the ones you linked to via a book selling place, are cheapened copies
of a pedal from the 80's..

This winter I got a set of Ergon pedals , though using plastics ,
they are not cheap
because the plastics were chosen for their engineered characteristics,
not cheapness .

Welgo is a decent pedal company, MKS a bit better.