These cover south-west Hertfordshire (including Watford, Rickmansworth, Borehamwood, Kings Langley, Abbots Langley, Bushey and Radlett), plus very small parts of Buckinghamshire and Greater London.
WD3 also covers the village of Chenies in Buckinghamshire, plus a small protrusion of Harefield in the London Borough of Hillingdon.
BUSHEY is a new post town; having previously been part of the WD2 district of WATFORD.
Bushey was to all intents a section of Watford sorting office; up until 2000, all mail for WD2 was cut and tipped at Watford office.
In order to change this, new codes were created to enable direct bags to be opened at Bushey delivery office.