In 1973, some major changes were made. Fine lattice (checkered) pattern was engraved on the top of the skirted spool caps on both sides. At the same time, the number 4 on the dial plate of the mechanical brake system on the left side returned to the same as earlier ones, in which the vertical bar of number '4' is long and the top part of '4' is closed.
The nuts on the right plate were also changed from those hand-screwed to those that need a screw driver.
The rims were also changed from so called 'grooved rim' to 'beveled rim' in 1973. Later ones such as #730902 (below) have the latter, simple 'beveled' rims.
Almost at the same time when the rims were changed, the drag wheel was also changed to one with square ends, but not simultaneously. I sometimes find one with beveled rims and a star drag with round ends.