Fathom MK & Gemini Head to Loop Connection Cap

Fathom MK & Gemini Head to Loop Connection Cap

Protecting the Threads That Matter

On Fathom MK series and Gemini rebreathers, the connection between the head and the breathing loop uses fine, exposed threads. Those threads are easy to damage and tend to collect grit when units are packed with other gear, stacked in bins, or moved between boats, cars, and hotels.

This Head to Loop Connection Cap was created to keep those threads protected during travel, storage, and long surface intervals - and to keep bugs, sand, and debris out of the head when the loop is removed.

Fathom Gemini Head to Loop Connection Caps

Designed for Gemini - Confirmed on MK

The cap was originally designed around the Fathom Gemini head geometry. After release, a Fathom MK3 diver confirmed that the cap fits the MK3 head perfectly, providing the same thread protection and secure coverage.

It fits MK and Gemini units released before November 2025. Newer production units use a bayonet-style connection, which is not compatible, and there are no retrofit options for that version.

Simple, Purpose-Built Design

  • Machined from solid Delrin - durable, lightweight, and resistant to impact.
  • Protects fine head threads from damage, grit, and contamination.
  • Vented design prevents negative pressure when used with a head cover.
  • Low-profile and travel-friendly - stays on during transport and storage.

A Natural Companion - Gemini Head Protective Cover

For divers looking to protect more than just the head threads, there is now a Gemini Head Protective Cover designed to work alongside this cap.

While the Head to Loop Connection Cap protects the delicate threads where the breathing loop attaches, the Head Protective Cover shields the rest of the Gemini head - including critical O-rings, sealing surfaces, and exposed O2 cells - during travel, storage, and surface intervals.

The two products are designed to be used together. The connection cap keeps the threads covered and vented, while the head cover protects the rest of the head from impact, abrasion, and contamination.

Used as a set, they provide full head protection when packing the unit in gear boxes, crates, or cases, or when storing the rebreather for extended periods.

Gear crate with Gemini heads with protective caps and covers on

Use Cases

  • Traveling with the breathing loop removed
  • Long surface intervals between dives
  • Storage in gear bins, crates, or cases
  • Keeping insects and debris out

Compatibility Notes

Compatible:

  • Fathom Gemini heads (pre-Nov 2025)
  • Fathom MK3 heads (confirmed fit, pre-Nov 2025)

Not compatible:

  • Newer bayonet-style head-to-loop connections

Additional Information

  • This is not an official Fathom accessory.
  • Designed in California, made in China.

Where to Find It

The Head to Loop Connection Cap is available at RUGGED SCUBA and ships from the U.S.

Photos and short videos showing fit on both Gemini and MK heads are available on the product page and Instagram.