For the halter or hackamore, we might need to have our hands out to the side more. For the snaffle bit, the hands are brought more toward the horse’s hip. Most people can put steady pressure on the snaffle bit rein, and the horse will likely give to it at some point.
The curb rein on a snaffle is always a little thinner than the snaffle rein. A normal bridle is used for both the pelham and the snaffle. Reins can be any type you want just as long as the curb is a little thinner than the snaffle. And is worm without a drop noseband, usually just a flat cavesson :)
The rings on a snaffle may be D shaped or have a small piece sticking up or down like a full cheek snaffle and Fulmer snaffle. The rings may slide or they may be fixed to the mouthpiece. The shafts perpendicular to the mouthpiece on the full cheek and driving bits prevent the bit from slipping through the horse's mouth.
If you are going to use a one ear bridle use a curb bit with it. I haven't had this happen but I know someone who was using it with a snaffle and the bridle managed to slide off while this person was riding. I like the browband headstalls the best. They stay on great and work for all western disciplines. I tend to see a lot of one and two ear headstalls at western pleasure shows.