It is possible, after reading our little review of the new Edelrid HMS Strike Slider locking carabiner that you wondered about the difference between a “normal” carabiner and an HMS version.

Let’s start with an assurance that it’s got not-a-thing to do with the service of any king, real or imagined. It’s fair to generalise that locking ‘binders come in three shapes; Oval, Off-set (or modified) “D” and HMS. The Oval shape is a bit old fashioned and while nice and simple fails to apply load to its’ primary axis (in fact it doesn’t even have a primary axis) and cross-loads too easily. The off-set design (typically the shape of snap-link carabiners used on quickdraws) is a vast improvement because it applies load allow the primary axis of the carabiner reliably and is more likely to turn, when rattling around on a protection system that is just coming onto load, toward its most favourable (strongest) orientation. The big disadvantage of the off-set shape is that it struggles to deal with more than one piece of rope (or carabiners clipped directly into it) at a time – ropes or ‘biners tend to pile on top of each other in an awkward, unseemly mess. The answer is the HMS shape which has a nice wide, evenly curved base that allows elements of an anchor to line up next to each other in an Honest, Mechanised Sequence.

Actually, that’s just nonsense. HMS stands for Halbmastwurf-Sicherung – German, roughly for “halfclovehitchsecuring”. Some countries in Europe through the ages have fallen on hard financial times during which the purchase of conventional belay devices became impractical, thus the use of a “belay knot” evolved – the Munter Hitch aka Italian Hitch, Crossing Hitch or Halbmastwurf. Unfortunately the off-set carabiner shape is unsuited to the Munter Hitch (it works but it makes the knot even more clumsy and oval carabiners went out with the war) so apparently one or another wealthy neighbouring European nation invented the HMS shape. Voila! Friends helping friends.

Ideally (seriously again) you could use an off-set shape for belaying a single rope through an ATC type device or with any auto locking belay device (or in situations where you want the extra security of your rope running through a locking ‘biner at a runner) – any time there is only one simple element at each end of the carabiner. Use an HMS shape for belaying double ropes (always through ATC type passive belay device), for tying Clove Hitches into or where you are connecting different elements of an anchor via a carabiner.

A couple of little – perhaps even useful – asides…
1/ a Clove Hitch will still hold security on an off-set ‘biner (or even a small snap-lock if you are in a pinch) but note which side of the knot is going to receive load and put that side against the spine/main axis of the carabiner and…
2/ the Munter Hitch is a pig of a belay knot. It’s awkward and it twists ropes terribly (be especially aware of this if you are forced to rappel multiple pitches on a Munter Hitch because the twisted rope/s will jam and tangle much more easily when pulling them down – I speak here from experience) but it’s much better than offering your dear climbing partner a body-belay (or abseiling a la Dulfer Sit). If you climb long enough on multi-pitch routes you will sooner or later drop or forget your belay device. Learn how to tie a Munter Hitch and then, like taking a raincoat to a crag, you might never, ever need to use it.

Note: Much of the historical wisdom in this article is derived from the internet. Please do not bet your house nor your spouse against its accuracy.