Spool cans: Three different styles of spool cans (left to right: 1,2 & 3).
Face Plates: Two types of face plates. The smaller thread guide loop is set horizontal, or guide set at a 45* angle and closer to V thread guide.
Cover Plates: Two types; one that is attached and pivots open, one the slides open and off. You can see two differences. The older machine, Eldredge badged H5862, on the left and the newer, National badged H53848, on right. Both plates have the R.K. Hohmann patent info and same patent dates 1911-1913.
Hook Design: I see differences in the hook design associated with the change in spool can design. Left is oldest style (H5862)-uses style #1 spool can, middle (H18934) is a badged Eldredge-uses style #2 spool can, right is the newest (H53848) badged National-uses style #3 spool can. Arrows point to the differences in each.
Spool Winder Arm: Subtle changes in the winder arm. Left is the older style on H5862 & H18934. Right is on the newer H53848-the extra lever assembly functions as a release lever that holds the spool wider up while also holding the rubber motor wheel off the hand wheel when winding a spool (this machine came to me as an electric portable with a motor, which I took off to put it in a treadle cabinet).
Base Leg Position: Style on the right (H5862) has the front left-side leg positioned near the front edge of the base (does not fit into the later style National treadle cabinet) and the other on the right (H18934)style has the front left-side leg back about an 2 inches from the front edge of the base.
Hand Wheel: Original-treadle non-electrified machine head has a heavier and slightly larger wheel (149mm outside wheel diameter, 16mm thick outer wheel ring) than electrified portable machines (145mm outside wheel diameter, 14.5mm thick outer wheel ring).
Badge Decal Name: Eldredge, National, Western Electric or Graybar (a badged Montgomery Wards brand)
Treadle Irons: Some with Eldredge, National SMCO, plain on side of irons.