These come in two sizes:
 
1/2" (the end is round) (this will also fit 5/8")
3/4" (the end is square)
 
Please pick which size you'd like for the add on. 
 
If you are ordering a long line, you would select 1/2"
If you are ordering a leash that's 5/8" width, you would select 1/2"
If you are ordering a leash that's 3/4" width, you would select 3/4"
 
If you ordered multiple leashes, please also indicate which leash you'd like to add it to.
 
*Please note this add on is not an option on any listing that includes a leash as you will need to add this separately.*