I'm slowly piecing together my ground tackle, and now that I have the anchor I am looking for a swivel that is in the same strength range as the chain I plan on buying (3/8 G4 with a SWL of 5,100lbs). Many of the 3/8 swivels I'm finding have SWL of 1870lb and a Breaking Load Limit of only 5,500lbs! These include Kong and Marpac (which are re-badged from an overseas manufacturer)
It sort of defeats the purpose of buying strong chain if it is attached it to an anchor with a wimpy swivel. At 3/8 even BBB has a SWL of 2750 and PF has a SWL of 2625.
The Imtra Corp brand available at Boaters World (online only) has a SWL of 4,500lbs.
The EBay user UnicornStainless has some stronger swivels. The 3/8-1/2 swivel has a BLL of 15,000, which should put its SWL right around that of the chain. (SWL is considered 1/3 BLL). $121.68 + 6.50 shipping
The Kong brand at West Marine says 5,000kg (~11,000lbs) SWL in a straight pull and 2,000kg (~4,400lbs) SWL in a perpendicular pull (model # 644.10 - maybe it is a heavy-duty model?). At $99 it is also cheaper than the other two.
It says: "SWL (Safe Working Load) as indicated on the packaging and swivel is indicative of Max Load and can be considered breaking strength if the swivel is subject to transverse (perpendicular) loading.
I bought the Kong from West Marine for now. Eventually I'll purchase another from UnicornStainless and move this one to the secondary rode.