While the D shaped carabiner and the HMS carabiner are almost identical in shape and style, their shapes are designed based on their very specific uses. Let’s dive into more detail.
The HMS carabiner stands for Henry Munter System carabiner, which refers to a hitch called a Munter Hitch, invented by Henry Munter. The Munter hitch is a half clove hitch belay hitch, which allows the user to apply friction descent with just using a rope and carabiner. The HMS carabiner was purposely designed to be compatible with the Munter hitch as it has an enlarged top half of the carabiner with a wider cut out in the upper corner along the major axis to allow for better rope contact.
Here’s a little primer on how to tie a Munter Hitch:
The D shape carabiner is slightly smaller and doesn’t have the enlarged opening in the upper corner on the major axis side. This carabiner is best used when needing to attach multiple eye terminations on one side of the carabiner with a single connection in the lower corner. Setups such as an open system MRS Blakes hitch on a split tail is a perfect pairing with the D shape carabiner. You can also use the D carabiner in a hitch climber system, but due to the D shape you can run the risk of unequal pressure on an eye and eye prusik, whereas an oval shape carabiner applies equal pressure from its symmetrical shape.
The HMS carabiner and D shape carabiner are similar in appearance but have different intended uses. Therefore, choosing the right carabiner for the job is important for safety and efficiency in various climbing and rigging scenarios.