Hmm.
The one on the left has both “ears” cantilevered off the handle and so each can bend at the neck.
The other 2 both have one ear reinforced by the handle, leaving only one cantilevered or bendy ear.
I guess the obstruction spanners must work like a pair of stilsons where the grip on the nut increases from the bottom jaw (the one welded to the handle) as the torque increases by virtue of flexing of the spanner jaws. As Robin says, the short jaw on the normal spanner can bend away from the nut so opening the jaws and reducing grip on the nut. I must go and make one immediately….!
Hmm.
The one on the left has both “ears” cantilevered off the handle and so each can bend at the neck.
The other 2 both have one ear reinforced by the handle, leaving only one cantilevered or bendy ear.
I guess the obstruction spanners must work like a pair of stilsons where the grip on the nut increases from the bottom jaw (the one welded to the handle) as the torque increases by virtue of flexing of the spanner jaws. As Robin says, the short jaw on the normal spanner can bend away from the nut so opening the jaws and reducing grip on the nut. I must go and make one immediately….!