The David De-Val neck collar looks & feels robust, its metal construction has no plastic or other such like components to weaken, snap or cause it to break. It was based on the Squire 440 Old English padlock which had a steel case construction, (plated) with an internal 4 lever lock mechanism, as well as having a raised brass key hole cover. It came supplied with two keys (PEF KB440) allowing it to be opened and locked. These locks were designed to be used any almost any environment as well as being designed to last.
Only the body of the padlock was used, the original locking top shackle was removed and a specially made large looped neck ring was put in its place. The neck loop ring was a stainless steel looped rod which was specially made for David to fit on to the collar. The neck collars he sold were each made one at a time and the construction and manufacturer, as well as alterations to the lock to fit it were all done by hand. This gives a uniqueness to each one made which you can see by the photos.
The ring loop & padlock are totally secure there was no way to remove this once it was put on and locked, Its operation as padlock remain unchanged only difference was that it had a larger custom shackle (neck loop) that went round the neck. The neck loop was large enough to go round the neck comfortably but small enough not to allow it to slip over your head even if your head was a small size. The horizontal clearance of the loop is 15 ½ cm and vertical clearance is 16 ½ cm Specific dimensions of the 440 lock are- Body width 51mm. Body Thickness 16.5mm.
Some hand drawings & photocopy illustrations of the neck collar in books and pamphlets appear to indicate a Squire 550 padlock being used, although the Squire 440 & 550 padlocks are the same size and dimensions the 550 body was made entirely of brass and to my understanding it was the Squire 440 padlock model that was used in the construction of the neck collars.
Additional information I am aware of suggesting a 550 neck collar was produced was indicated is a grainy photo in a later advert pamphlet. This showed a 550 stamped padlock with no neck loop attached where you would expect to see it. In the photo the normal shackle area is obscured with a box of typed information which was overlaid, based on this it was most probably used for reference to the locks operation and was not an actual neck collar.
The loop ring was secured at the right side of the lock and was permanently hinged there, it moved over to the right when the ring was opened to allow the locking catch on the other end to disengage out the padlock body when unlocked using the key. There was a small washer in place here to ensure the loop did not move to freely once open, then it was able to be fully opened very wide approx 27-29 cm The Original shackle thickness was 8mm, Neck Loop thickness is also 8mm