In November 2025 Fathom changed the head-to-loop connection on the MK and Gemini from a fine thread to a 2-start bayonet. If you have one of the newer units, the original threaded connection cap does not fit it. So we made a new one.
Different Connection, Different Failure Mode
The bayonet lugs are tougher than fine threads, but the sealing surface behind them is just as exposed. Sand or grit sitting on that surface when you mount the loop is what actually causes problems. The cap covers the lugs and the sealing face, and takes the hits when the head is packed against tanks, weights, and everything else in a gear bin.
It also does the unglamorous job of keeping bugs out of the head between dives. If you have ever found a spider setting up shop in your loop connection, you know.
Machined In-House
The threaded cap was designed in California and machined overseas. This one is machined from solid Delrin in our own shop in Los Angeles, start to finish. Shorter iteration loop, tighter control over fit, and no waiting on a container when stock runs low.
Two Colors
The cap is available in black and in natural Delrin, which is white. Same material, same dimensions, no dye. If you color-code your gear or just want the cap visible in a dark gear bin, natural is the one.
Details
- Machined from solid Delrin
- Vented, so it will not pull a vacuum against the head
- Available in black or natural (white)
- Sold as a single cap or a set of two
Which Cap Do You Need?
Bayonet connection (units made November 2025 or later): this cap.
Threaded connection (units made before November 2025): the threaded version. The two are not interchangeable in either direction.
If you are not sure which head you have, look at the loop connection: lugs and a quarter-turn action mean bayonet, continuous fine threads mean the original.
Where to Find It
The Bayonet Head to Loop Connection Cap is available now and ships from the U.S.
This is not an official Fathom accessory.
Designed and made in California.