What do the various numbers mean on the spool ends?

A 932 prefix denotes 30 wt. rayon. A 942 prefix is 40 wt. rayon. 962 is Poly Deco polyester. A 972 is PolyLite 60 wt. Polyester. If the 3-digit 900 prefix ends in 3, it represents a king size spool. The 3 or 4 digits that follow the 900 prefix represent the color number.

Sulky Sliver Metallic has a 145 prefix; Sulky Original Metallic small spool has a 142 prefix; and the king size spool has a 143 prefix.

Sulky Cottons have a 700 series prefix:
713 identifies 12 wt. Cotton.
733 identifies 30 wt. Cotton.

Solid Color Cottons have a matching color number to the Rayons. For instance, 1001 Bright White is the same in both Cotton and Rayon, and the 3-digit prefix identifies the TYPE of thread.

Sulky Cotton Blendables all have 4000 series color numbers with a 3-digit 700 series prefix:
713-1001 would mean it is a 12-wt. Cotton in 1001 Bright White.

We also now have 50 wt. Cotton+Steel by Sulky in 100 solid colors and this quality sewing thread has a 753- prefix. 

The 12 wt. Solid Color Cottons now also come in convenient and economical 50-yard spools called Petites.  There are also 30 of the 12 wt. Blendables in this size put-up.

Jumbo Cone 3-digit Prefix Identification:
940 - 40 wt. Rayon
930 - 30 wt. Rayon
960 - Poly Deco
730 - 30 wt. Cotton
710 - 12 wt. Cotton