Hoya may have made them for a third party. Camera company. Retailer etc.

If you're worried have you considered step up rings?

http://cgi.ebay.com/ws/eBayISAPI.dll...511545747&rd=1

If you think the price for the 48mm are bad you don't want hear what they wanted for a 35.5mm to 49mm step-up ring. I ended up using two rings. Jim pointed me to one for a little digital camera that cost a couple of bucks-)