I've seen a few that have had a non-adjustable striker setup, they are however pre-loaded during the build..... these boats have been in the 1650 numbers and up

Both my mozzies do have an adjustable striker as does the plan set I have which specifies a 5/16th stainless bolt with locknut & adjuster nut being tig welded to the down tube under the mast step.

I recall breaking a bolt on my first mozzie (245) way back when....