Note - Chicago screws are two-piece metal fasteners sometimes found on bridles and other tack. They are flat on one side, and have a straight-blade screwdrive slot on the other side. One side screws into the other.
Do y'all leave the halter/lead rope on when you go out? I do, and it came in very handy yesterday. I just coil up the rope and tie it (with a little strip of leather) to my (English) saddle, leaving it clipped to Sabrina's halter. I've had a couple of times I've used it, like, finding a kitten on the trail (my first ride out with Sabrina), and leading her and Cooper back while Christi carried the kitten. And if anything goes wrong with the bridle, I could always pull her head around with the lead rope and turn her to slow/stop her (she's used to this from riding in the yard with just a halter).
So the other day I went for a short ride up the road, with Michael coming along for a walk. I did the usual hop-on-and-trot (we're working on standing for mounting...) and trotted down the driveway and turned up the road. Something wasn't right, and it looked like the cheekpiece had come undone (How? I had just fastened it.) I asked her to stop, and she did (odd...), and when I looked again the bit and most everything else was hanging below her chin. Middle of the road, no bridle, cool evening, *forward* horsey... Uh oh. Miraculously she stood there calmly and Michael was able to take hold of the lead rope while I dismounted. Turns out a Chicago screw (which should be banned, IMHO) had come loose. That'll teach me not to check *every screw, every time*.
We went back, put on a different bridle, and went for a nice walk/ride.
We would have been in a real spot though if I didn't have that halter on her!
Right after you check all your tack with Chicago Screws, check you tire pressure and lug nut torque on the trailer. Just in case. :-)