The 3/0 thread is multi-filament thread, suitable for flies larger than size 12. The 6/0 and 8/0 thread is made of continuous polyester filaments slightly bonded the filaments are not twisted and tie virtually flat on the hook.
Strengths : 72 denier (8/0)  135 denier (6/0)  180 denier (3/0)
Lengths :  200yrds (8/0 & 6/0) 100yrds (3/0)