Looking at your pictures and being unfamiliar with the Stillpoints. I am curious if the stud can be removed from the Stillpoints? If so the I would remove them and drill and tap the new holes to accept the 3/8" thread you need.
I think and adapters are going to eventual force the 1/4" stud to fail. Just my immediate impression upon looking at the pictures you posted.
I think and adapters are going to eventual force the 1/4" stud to fail. Just my immediate impression upon looking at the pictures you posted.