Guide to Tinsel Sizes.
Colin Campbell from Mauchline in Ayrshire sent a useful card to FF&FT magazine which seems to have come from an old Hawkes & Black guide. You may find it handy when sizing numbered tinsel spools. It relates to spools of flat tinsel, embossed tinsel, oval tinsel, round tinsel, lace twist, and copper and lead wire.

No  inches  inches      mm
1  .012    1/80 in       0.30
2  .015    1/64 in       0.40          FLATS Gold or Silver (Sizes 1-11)
3  .023    1/40 in       0.60
4  .030    1/32 in    0.80          LUREX Gold or Silver (Sizes 2,4,5)
5  .040    1/25 in       1.00
6  .043    1/23 in       1.10
7  .048    1/21 in       1.20          LUREX (all colours) (Size 2 only)
8  .052    1/19 in    1.30
9  .060    1/16 in    1.60
10  .072    1/14 in    1.80          EMBOSSED Gold or Silver (Sizes 3-11)
11  .075    1/13 in    1.90
14  .020    1/45 in    0.50
15  .022    1/40 in    0.55
16     .030    1/32 in    0.80          OVALS (Flat Worm) Gold or Silver
17  .035    1/28 in    0.90             (Sizes 14-19)  
18  .040    1/25 in    1.00
19  .058    1/15 in    1.50
20  .007    1/140 in     0.20          ROUND THREADS Gold or Silver
21  .010    1/100 in     0.35              (Sizes 20 and 21)
22  .016    1/64 in    0.40          LACE TWIST (3-ply cord) (Gold or Silver)
23  .020    1/50 in    0.50              (Sizes 22-24)
24  .022    1/45 in    0.55          WIRES  
25  .006    1/165 in     0.15          Gold or Silver (Sizes 25-27)
26  .005    1/200 in     0.12          COPPER (Fine or Heavy)
27  .004    1/250 in     0.10          LEAD (Fine)