The port sockets of some different makes of camera housings are identical, something I only recently noticed while working on my Sea&Sea and Isotta housings (Fig 1). When I looked up these compatible port sockets and bayonet plugs, I found that they are labelled 'B120' for the bayonet's outer diameter of 120 mm. Items made to the B120 standard allow one to mate housings of one make with the ports of another, such that my Isotta's adapter for Subal ports fits my Sea&Sea housing.
Adapters for other sizes of equipment are available. For example, a suitable adapter will mate Subal lens ports with 97 mm o.d. bayonets to the B120 mount of an Isotta or Sea&Sea housing.
I looked up interchangeable adapters and found the following:
The B120 Isotta Subal Type 3 port adapter lists for $250 US, and the Saga Sea&Sea housing adapter for $335 US (1, 2).
Isotta also has adapters for Seacam, Subal Type 3 and Type 4, Aquatica and Hugyfot ports (3) and B120 extension rings, some with a focus gear (4).
Sea & Sea has B120 adapters and ports with B120 fittings to mate with Isotta housings. Backscatter states: "Isotta housings use a simple port system, which is identical to Sea&Sea's method. The good news here is that Sea&Sea brand ports are fully compatible, so if you have any in your arsenal they will carry right over. You could also run a Nauticam port as long as it has a Sea & Sea style bayonet mount on it, so right out of the box you have tripled your port options." (5).
Nauticam housings have B120 adapters for Subal and other ports, and Nauticam N120 ports may require an adapter to be B120 compatible (5).
The B120 mount is made by several (but not yet all) underwater housing manufacturers. Let us hope the versatility of the B120 standard for bayonet and socket mounts, and the B102 and M67 standard for metric threads, continues to be adopted by more makers of UW photo equipment, as it will benefit all of us underwater photographers.
References:
1. https://www.isotecnic.it/en/adaptor-ring: Isotta Adaptor ring for Subal Type3.
