I have a Super Ricohflex, and I use this website as my reference:
They say that the filters are Bay 1:
The original Diacord model (a.k.a Ricohflex Dia) as well as the Diacord G and L and Ricohmatic 225 have a cast aluminum body and helical focusing with a lever on each side of the lens panel (called "Duo-Lever Focusing System" in the Diacord G manual.). Better shutters were used giving more speeds: 1/10-1/300 (Dia), 1-1/400 (G) or 1-1/500(L and 225). The lens in the Dia is a 3 element design (AFAIK) and some Diacord G's have a 3 element Riconar lens. Later G's as well as the L's and 225 have the well regarded Rikenon 4-element (tessar style) lens. The Diacord models still use knob advance with separate shutter cocking levers, but the 225 uses a crank to wind and simultaneously cock the shutter. All models have automatic stop on the next frame and thus don't have the red window. They use Bay 1 filters and accessories (except for Dia). Click here if you want to build your own Bay 1 lens shade.