Bolt in Tun
a public-house sign, is heraldic. In heraldry it is applied to a bird-bolt, in pale, piercing through a tun. The punning crest of Serjeant Bolton, who died 1787, was “on a wreath a tun erect proper, transpierced by an arrow fesseways or.” Another family of the same name has for crest “a tun with a bird-bolt through it proper.” A third, harping on the same string, has “a bolt gules in a tun or.” The public-house sign distinguished by this device or name adopted it in honour of some family claiming one of the devices mentioned above.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894