The Bridlework you choose should be to do with the size of your Horse or Ponies head and the competition or sport you are participating in.
A substantial Horse is going to look completely wrong and under bridled in ½” Bridlework and at the other end of the scale a tiny Pony is going to look swamped in ¾” width Bridlework.
A suggestion would be small ponies and very fine larger ponies should have 1/2" bridlework and larger poinies and small or fine headed horses 5/8" and larger Horses and Cobs 3/4" Bridlework
The size of your hands denotes what width of reins you choose, reins must feel comfortable to hold and you must be able to use them sensitively and effectively and be able to close your hand around the reins. As a general guide when using a single rein on a Snaffle or other type of Bridle.
A child or a small lady with small hands will probably be more comfortable with reins that are ½” in width.
For an older teenager or average lady reins 5/8” in width will feel more substantial.
A man with much larger hands is going to be more comfortable with 3/4"
When riding with two reins on either a Double Bridle or a Pelham Bridle.
A neat Show Pony or an Arabian you may consider ½” reins for both your Bradoon Rein and your Weymouth Rein.
A Larger Pony or Small Riding Horse, 5/8” for your top rein and ½” for your bottom rein.
A Large Hunter ridden by a Man could have ¾” as a top rein and 5/8” as a bottom rein.