How much can ball handler use his arm?

[Rob1968]

Let's take a look at 4-24-5 . . . "It is not legal to use hands on an opponent which in any way inhibits the freedom of movement of the opponent . . ."
And, more the to OP-
4-24-7 . . ."It is not legal to use the hand and/or forearm to prevent an opponent from attacking the ball during a dribble or when throwing for goal."
Of course, Basketball Rules Fundamentals 10. applies..."Personal fouls always involve illegal contact . . ."

Many coaches teach ballhandlers to set the off hand/forearm, in a position to discourage the defender from reaching in, and it becomes a moment of judgement by the covering official as to whether contact on that arm constitutes a foul, by the offense or defense.