I was under the impression from doing online research Sinar and Horseman lens boards were compatible. I bought a Horseman lens board from KEH and here is the exact KEH label: Horseman 4x5 32 hole board (Sinar). When I received it it didn’t mount on my Sinar spec standard but another actual Sinar brand board did. I asked a camera repair/machinist and he said they boards are close but not the same.