This option is for those who appreciate a little more freedom of movement or utilize their legs to hold tongs or other tools while forging. The top of the split is secured with a riveted strap. You choose the length that works for you (based on a 36" long apron). ***NOTE: Lap aprons include the split at no additional charge.  
Our headless model in most of these photos is my husband who is 6 foot tall, 190 lbs. He is long legged. A 12" split fits him well.  If you are shorter, a longer split will work. If you are taller, go with a smaller split length. The super-soft leather is akin to a heavy sweatshirt. It will lift and fold fairly easy when you put your tongs between your legs. If in doubt, a shorter split length is better as you don't want to expose your groin area.
You can figure out your ideal split length by measuring from the top of your chest, where you think your apron will most likely start (usually in line with the top of your armpits) then measure down the length of the apron you are ordering. Original Cut and Full Cut are 36". The Mid-Length is 31". Or to a custom length you have chosen. That will show you where the bottom of the apron will lie. NOW, measure back up toward the groin to the top of where you would want the split to end. That will give you your split length. Ideally, allow at least 3" from split top to groin. Again, it is better to be shorter than too long and expose the groin.