Green’s Dictionary of Slang

1. false teeth [clacker n.¹ (2)].

1950, 1965–70		in DARE.
2007		S. Maloney Sucked In 91: Dentures were virtually standard issue [...] You got a full extraction and a pair of clackers on your twenty-first birthday.
2024		J. Meades Empty Wigs (t/s) 190: Oh, they’re [i.e. old women] all up for it at heart even if they do have to [...] remove their store-bought clackers the better to show their affection.

2. the breasts.

1963		C. Thomas Not Quite Posthumous Letter 8: I have positively not an ounce of physical vanity left: my clackers can rattle down to my flat feet and my wig drop off in front of the howling mob for all I care.
1986		M. Howard in Men Only 51 1: Errol Flynn commenting of joan Crawford’s breasts: ‘How about those for a pair of clackers, eh, sport?’.

3. testicles.

1997		Wired mag. Mar. 85: Smash his clackers and call him Sporano.
2003		PC Zone Mar. 149: Manholes you could throw the enemy into after kneeing them in the clackers.
2012		E. Kestner That Book about Harvard 251: I’m freezing my clackers off out here!
2016		N. Cummins Adventures of the Honey Badger [ebook] This big bastard [i.e. a kangaroo] had clackas like cannonballs, an absolute monster.

4. (Aus.) speed, mechanical power.

2016

N. Cummins Adventures of the Honey Badger [ebook] This boat had some clackers and pretty soon Bruce and his sidekick Matt had us on a spot.