Do you mean M48 x 0.75 threads? If so, that is ACC07. See https://diffractionlimited.com/product/adapter-plates-compact-cameras/
I have this flattener, https://www.stellarvue.com/sffx1-flattener/ And it has M48x.75 threads. The current plate on my OAG has M42 threads, so it looks like that is the plate I need. Thanks!