ESF, like the KAC product before it, incorporates QD swivel sockets on the end plate and the two products share a common outline, which often invites comparison of these two similar products. We don't usually pitch our product against one made by another company, but since this seems to come up often, a detailed explanation is called for.
ESF's shape isn't based on KAC's end plate/sling adapter, but on TDP spec carbine end plate, and its QD swivel housing was dictated by the requirement to host 3 sockets, which turned out to be quite complicated. Both ESF's and KAC's end plate/sling adapter's forms follow the function for which they're designed. In retrospect, there may be ways to make ESF look more different, but we always choose the simplest and most direct route, which is usually the most efficient shape, this happens to be the same as KAC chose. Making ESF look different wouldn't have improved it even marginally, so that thought never crossed our minds.
Familiar aesthetics aside, there are some key functional differences.
ESF's stated objectives are as follows:
1. Must use a standard castle nut that can be staked
2. Must allow a carbine stock to fully collapse (on the RE's #1 position)
3. A rear facing QD swivel socket
4. Options for either rotation limited, or non-rotation limited side facing sockets
We recently compared an ESF to the KAC end plate/sling adapter. When placed side by side, the differences are rather numerous and obvious.
1. ESF's "ring" is narrower (it's TDP spec), in order to accept a standard castle nut and allow the stock to fully collapse
2. ESF's QD swivel housing's top corners are higher
3. ESF's QD swivel housing is deeper to accommodate the rear facing QD swivel socket
4. When completely installed, there is almost no space between ESF's QD sockets housing and castle nut.
The high top corners and tight tolerances of the QD housing serve as a backstop. Should undue pressure be exerted and ESF's "ring" portion starts to bend, the QD swivel housing will immediately bottom out against the castle nut and stop its travel.
We used a prototype 7075 ESF and a well used KAC end plate/sling adapter for the following comparison pictures.
A top view comparison.
Viewed from the side
ESF's socket housing is slightly widened to accept a rear facing socket
A rear view of both