These were very popular alternatives to buying individual Bay1 Rollei filters. series 5 and 6 filters were much cheaper and readily found. Entire sets can be had here on e-bay for a few bucks. Series V adapter bayonets directly to all Rolleicords and Rolleiflex models with a f3.5 Tessar or Xenar lens. It also fits Yashica and Minolta Autocord TLRs. A series V lens hood can also be screwed on to the adapter. If you have series 6 filters, the 5-6 adapter can accomodate those larger diameter filters too. The series 6 retaining ring is a little rough but is still useable. Domestic postage will be $4.