50 Pence Trial

The 50 pence piece did not officially enter circulation until 1969, but pattern and trial strikes were produced in advance to test the heptagonal design — the first seven-sided coin intended for general British circulation. The Reuleaux heptagon shape was specifically chosen because it rolls at a constant diameter, allowing vending machines to accept it without modification despite its irregular outline.

This 1967 trial predates the decimalization switchover by four years.