Wire Thickness
Determining Wire Thickness - Option 1 Measure in millimetres over 10 coils and divide by 10. For example if 10 coils measure 85mm, the wire thickness is 8.5mm
 
Spring Handing
Normally, a right hand would spring is mounted on the left hand side of a door (when viewed from the inside). The left hand wound spring is mounted on the right hand side of the door (when viewed from the inside). This is NOT always the case and it’s recommended that each spring is checked individually.
 
Use image above if unsure
 
Further info can be found at: 
https://www.indupart.co.uk/wp-content/uploads/2019/06/Spring-Information.pdf