Matthew Poole and continuators on 1 Chronicles 29:24

24 And all the princes, and the mighty men, and all the sons likewise of king David submitted themselves unto Solomon the king.

Heb. Put their Hands under Solomon, i. e. They owned him for their King, and themselves for his Subjects, and sware Fealty to him; which possibly they now did after the ancient manner with that Ceremony of putting their Hands under his Thigh which was used in Swearing, Gen. 24. 2. & 47. 29. or at least the thing is signified by a Phrase taken from that practice formerly used, though now neglected; it being usual in all Nations and Languages to signifie present things by Phrases taken from Ancient Customs.

Marginal references: Heb. gave the hand under Solomon, Gen. 24. 2, 3. & 47. 29.