Not a very bright question... DMSB line must be strong enough not to break. Apart from that, it should be 2 mm If thinner than 2mm can get entangled, while if thicker than 2mm it can be difficult to roll it up on the spool. Are the lines commonly used for scuba made of a specific material or any similar nylon line will do?
I found this one for example
Leroy Merlin
Filo nylon alta visibilita
Plain 2mm nylon line, yellow color...
I found this one for example
Leroy Merlin
Filo nylon alta visibilita
Plain 2mm nylon line, yellow color...