TT #626 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:03
Forty times he shall strike him; he shall not add, lest he continue to strike him beyond these with a great blow, and your brother be degraded before your eyes.
Torah Temimah points to Makkot 23a.
TT lemma: יַכֶּנּוּ.
English: ‘He shall strike him’ – they flog him with a strap of calf-hide, for it is written ‘forty times he shall strike him’ and adjacent to it is ‘You shall not muzzle an ox while it is threshing.’
Semikhut (juxtaposition of the two verses) — not a formal named middah of the 13; the adjacency supplies the material of the strap.
The instrument of flogging is a strap made of calf-hide, derived from the adjacent verse about the ox.