Credit SCF Member Cfrphoto:
Flat plate coils were cut from partly perforated sheets into strips. The strips were pasted end to end to create coils. Paste up pairs and center line pairs occurred at the same frequency, every 20 stamps. Hand assembled coils were cut into strips before pasting up the strips into coils. The half sheets were pushed through a specially equipped perforating machine with cutting wheels resulting in parallel, but very slightly irregular edges very different from later "Auto Wound" coils stripped by the Stickney coiler. After it was was available, half sheets were pasted up before stripping into ten coil rolls. The sudden appearance of perf 8½ coils can be attributed to the fragility of the perf 12 half sheets pasted up into a continuous web for stripping. Few perf 12 Auto Wound coils were produced. Later, when sheet stamps were changed from perf 12 to perf 10, flat plate coils were also changed, but the production run was short because they were soon replaced with rotary press coils.
Rotary press paste up pairs could occur if the web broke and was repaired but they are uncommon.