Green’s Dictionary of Slang

1. the testicles.

1958		(con. 1940s) B. Behan Borstal Boy 172: No catching by the cobs.
1963		C. Wood ‘Prisoner and Escort’ in Cockade (1965) I iii: Think of Jim Blake satisfied, adjusted, and laughing little cobs.
1999		Roger’s Profanisaurus 3 in Viz 98 Oct. 8: cobs n. Nads; pills; pods. Testicles.

2. see cobber n.²