Used to call them service stripes in my day.
They were generally seen in places like The Brigade of Guards and Kings Troop. Some RA Regt's also used them.
We had a lad turn up with two of them and I was detailed to find out the regs pertaining to this.
After trawling through the 1955 Army Act I discovered that ; You got your first one after two and a half years. The next one came after another two and a half years and any following ones every five years thereafter.
You were only allowed to wear them up to the rank of L/CPL (L/BDR) and if you made full screw they came off.
I remember seeing some bandy Lance Jack with four of them.