The current design for the five-Baht coin was introduced in the mid-1980's. Before that, the coin was larger than the current 10-Baht coin. You will generally only encounter the really old coins at 'antique' stalls.
The Five-Baht coin - Kanchanapisek version.
The Kanchanapisek coin was issued to commemorate the king's 50th anniversary on the throne.
The oldest version of the small five-Bhat coin.
This original version of the smaller five-Baht coin featured the prow of a Royal Barge on the back, with the Grand Palace in the background.
Samples of older larger five-Baht coins.
The old five-Baht coins were huge, but this was 20 years ago when five Baht bought you a meal at a roadside stall. These coins display a garuda on the back.