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: