Tolerances are + 0.1 mm
Material... Most softwoods are suitable, but the type 2A and type 2B were always made in hardwood for extra strength and resistance to warping.
Standard Top bars... upper is the alternative type, lower is the original 'standard' type.
Apex type 2B Top bar
In order to limit the places where wax moth could pupate, the central groove did not run to the ends, but finished at a point that was covered by the side bar.
Apex type 2A Top bar
This 2A type was manufactured in two forms... The one shown here was used for cut comb production. The other type (future link) was without a groove, had drilled holes and was used to mount pairs of half width breeding frames for use in full sized brood boxes.
Top bar for drone frames