There were a few different versions of the ceramic line spreaders and getting a matched set nowadays is a good prize. Most of them had a shallow groove at or near the end, in addition to the hole. The old buzzard method of making open wire line was not to thread the spacers onto the wires, but to lay them up against the groove and use a short tie wire through the hole and wrapped a few times around the main wire. It was considered good practice to solder these connections. That way, nothing can slip or slide and it all works well when airborne. Using clips or other devices would add weight to the assembly and that's not what you want.
73 de Norm W1ITT
From the "Handbook"...