I have used Vixen CW's before with HEQ5 without issue. The Vixen hole is 19~20mm, so it accomodates the 18mm HEQ5 shaft properly (seeing SW copied Vixen standards).
Not cheap, but correct and small diameter compared to those horrid SW lumps
https://myastroshop.com.au/products/...p?id=MAS-033L2
https://myastroshop.com.au/products/...sp?id=MAS-033M
https://myastroshop.com.au/products/...sp?id=MAS-033L
https://myastroshop.com.au/products/...sp?id=MAS-033N