Wrong planchet (off-metal) Coin Errors
What is a wrong planchet (off-metal) error?
An off-metal or wrong-planchet error occurs when a planchet of the wrong size or composition is fed into a press striking a different denomination. The dies impress the design but the coin shows the wrong metal, weight, diameter — and often the design is incomplete because the planchet is too small. Major UK examples include £2 designs struck on 50p planchets, and 50p designs struck on 20p planchets.
How to spot one
- Compare the coin's diameter and weight to the official Royal Mint specification for that denomination.
- Off-metal coins often have weak or incomplete strikes because the dies don't fit.
- Colour mismatch is a giveaway — a "£2" struck on cupronickel has a uniform silver appearance instead of the bimetal gold/silver split.
- Verify with weight and diameter measurements before assuming an error vs a counterfeit.
Authentication
PCGS, NGC and CGS UK certification is essential for off-metal claims. Counterfeits are extremely common — many "wrong planchet" claims are gold-plated or post-mint altered coins.
Famous UK examples
Several documented examples; bimetal £2 design struck on a single 50p blank.
Reverse mistake — 50p design on the bimetal £2's inner cupronickel disc.
Key-date UK coins worth examining
Errors on key-date coins compound rarity — the host coin is already scarce, and the error multiplies the value. Browse the rarest UK coins in our catalogue: