“Afterward Hezron went in to the daughter of Machir the father of Gilead, whom he married when he was sixty years old. She bore him Segub. Segub was the father of Jair, who had twenty-three towns in the land of Gilead. But Geshur and Aram took from them Havvoth-jair, Kenath and its villages, sixty towns. All these were descendants of Machir, the father of Gilead.”
The oldest son of Manasseh was called Machir, who became the father of Gilead in Joshua, chapter 17. He also was active in the conquest of Gilead in Numbers, chapter 32. Thus his daughter would be a cousin of Hezron and make Hezron more powerful. There is another Segub who rebuilt Jericho, but otherwise this Segub goes unmentioned. However, there were a lot of people named Jair. First there was the 7th judge who had 30 sons, judged for 32 years, and had 30 cities in Gilead in Judges, chapter 10. Obviously this is the reference here but there was no mention of his father in Judges. There is a reference to the Geshurites and the Arameans who took these 60 towns from Gilead in the period before the Exile. The main reason for this mention was to relate Hezron to Machir and the land of Gilead.