Green’s Dictionary of Slang

digger’s delight n.

[digger n.1 (2) + SE delight]

(N.Z.) a wide-brimmed felt hat.

[UK]Barrère & Leland Dict. of Sl., Jargon and Cant.
[UK]Farmer & Henley Sl. and Its Analogues.
[Scot]Dundee Courier 3 Mar. 8/1: The Hat in Slang [...] A by no means exhaustive list would include ‘tile,’ ‘golgotha,’ ‘canister,’ ‘castor,’ ‘chimney,’ ‘colleger,’ ‘cock and pinch,’ ‘cowshooters,’ ‘david,’ ‘digger’s delight,’ ‘fantail,’ ‘gomer,’ ‘goss,’ ‘moab,’ ‘molocher,’ ‘muffin cap,’ ‘mushroom,’ ‘pill box,’ ‘stove pipe,’ ‘thatch,’ ‘truck,’ and ‘wee jee’.
[Aus]Baker N.Z. Sl. 46: Digger’s delight, a large felt hat worn by gold-diggers in New Zealand.