I wish that everyone reading this could have the experience of feeling an equine penis.
It isn't like a canine penis that stays moist in a sheath. It's soft and dry and built to be out in the weather. It's similar to a human penis, with a nice beefy feel. It does stay in a sheath but it's easily coaxed out. The sheath is soft to the touch, and then the head of the penis emerges to fill your waiting palm.
As with humans, every one has its own size and shape. But an equine penis might be black, or pink, or some splotchy mix of grey, black and pink. Worthy of study just for that.
It's amusing how sometimes horses will "drop" without any sexual activity. It's just a nice day to have your penis hanging out. They're not hard when they hang like that; they have a nice thick feel. Then they can snap to hardness in a heartbeat.
If humans could flare, porn would be more interesting.
One thing about playing with equine genitalia is, you can clean it as you play. It does a favor to a horse if you rub his penis and knock off crust. There can be "beans" of ... stuff ... and you can pick those off.
If the horse doesn't want contact, he can flinch away and cow-kick forward. He can swing his head around and bite you. In my experience, maybe 75% of them enjoy a belly rub and a sexual massage. It's a form of grooming.