Originally posted by
21 reviews here: link I'm sure at the very least one of them will answer this question.
The second review that I clicked out of the 21 available had this information.
from review by Eva Schwaltz (link here: link
"The head is 4” in circumference, then the shaft narrows down to 3 3/8” in circumference, and the base of the shaft is 5 ½” but it’s difficult to insert this far anyway."