It is doubtful that a correctly proportioned toggle clasp will come
open of it’s own accord. Not impossible ,but extremely unlikely. For
the toggle clasp to be made correctly there are two basic important
considerations to be followed.
First: the circle (square, triangle or whatever) portion of the
clasp should have an inner opening just large enough to allow the
toggle bar and jumpring, offset, and endcap to pass through it. If
there is too much open space it will slide through too easily and the
clasp will be “sloppy”.
Second: the length of the toggle bar does have a proportionality to
follow for it to be secure. When the clasp is closed the bar should
be long enough to extend securely past the outer edge of the circle
when the center of the bar slides to either side of the circle. That
way the bar must be pulled all the way through the opening and
folded against the chain to pass back out and open the clasp.
Having the toggle bar extra long won’t accomplish any advantage if
the first consideration isn’t applied, other than making the clasp
more difficult to open.
Many commercial toggle clasps are not proportionally well designed.
It is quite simple to make one from scratch.
Michael David Sturlin