The hand that held my wrist Was battered on one knuckle; (lines 9-10)
The father has rough hands, which show that he's a working man. We know that, in real life, Roethke's father owned a greenhouse and a timber preserve. In this poem, rough hands that work in the dirt demonstrate this father's manliness.
At every step you missed My right ear scraped a buckle. (lines 11-12)
In the early 20th century it was common for a father to discipline his kids by beating them with his belt. Punishment like that isn't explicitly shown in this poem, but we wonder if this same belt has been used to discipline the boy as well.
With a palm caked hard by dirt (line 14)
This line shows us again that the speaker's father works hard with his hands, making him seem manlier. We wouldn't think that these hints about hardened, battered hands were so important, except now we've heard about them twice. The hardened working hands stick out in the memory of the speaker of this poem.