This sign appears on all new Ifor Williams trailers - have you read it? The top section sections says that no horse or pony is to be tethered to the outside of the trailer or transported in the area adjacent to this door. In other words, horses should not be travelled in the trailer without a front breast bar - either half or full width. The reason for this is that having the horse (able to go) further forward affects the nose weight of the trailer on the tow bar and seriously affects the stability of the trailer and the towing vehicle.
These eyes, which are provided in order to make it easier to undo and drop down the breast bar from outside should never be used to tie the horse up. Any strain on them can distort the structure of the trailer and could also affect the ability of the bars to be dropped down in an emergency.
Older Ifors have these at the front instead of eyes, and all Ifors have them at the back for the back bars; it is cheap and easy to replace all of them with the new eyes which can be obtained from an Ifor dealer. It's important to make sure that these older 'screws' have not seized up and that you know where your Allen key is kept.
The correct way to fasten the front bars, which is clear in all Ifor literature, but not particularly highlighted, is with the fastener to the OUTSIDE of the trailer as shown above as this means that if the bar is released from the outside using the Allen key or by turning the eyes, it will drop down to some extent whereas if the hinged part of the bar is to the outside, it will not.