The headword is indeed a farming tool with three tines, but it is not a mattock as the LSJ indicates s.v. tri/nac (web address 1); see next note.
[1] Greek Anthology 6.104.6 (Philip), the farmer Lusixenos's dedication to Demeter; cf. Gow and Page (vol. I, 310-311); (vol. II, 343); and further excerpts from this epigram at alpha 4721, beta 455, gamma 54, upsilon 120, omega 69, and omega 81. The three-pronged implements that Lusixenos consecrates here are pitchforks or winnowing forks, which are used to toss ears of threshed grain into the wind so as to remove the dried husks; cf. Gow and Page vol. II (126), Paton (354-355), Greek Anthology 6.94 (Antiphilus), and theta 498 note 3.