Rim/Edge Juncture. The point where the horizontal plane of the face of a struck piece meets the vertical plane of the edge. This point is most angular in proof coinage with a sharp 90° angle. In production run struck pieces it may exhibit a slightly rounded or bevel corner since the metal does not flow to that exact point. If the planchet is oversize, or there is too much pressure exerted by the dies, then metal will flow out at this point (it is the only place for it to go). This anomaly will create a burr or flash (also called a wire edge in America or knife edge in England). Continued striking with this problem would probably break the collar or the die. The closest word to the concept of rim/edge juncture is the architectural term the sharp edge where two surfaces come together (but either surface may be curved, not necessarily one surface flat like coins and medals).

In 1961 an English numismatist made a study of the rim/edge juncture of British 12-sided (dodecagonal) three-pence pieces of 1937-52. He found that what was once "sharp" with a full rim/edge juncture changed to "rounded" edges (during WWII but gradually returned to sharp edges by 1950). This was explained as the breaking of the collar at one of the 12 corners in the collar due to lower quality steel for dies available in wartime. When high quality steel became available (1948) this problem was eliminated (but old collars were used for the two-year period until they too became unserviceable).

Reference:

C36 {1961} Larsen