"hook onto" is correct and usable in written English.
You can use it to indicate that someone or something is attaching to something else, such as "The climber hooked onto the rope".
"The better to hook onto the pedals," she said.
In repose, the inner edges of the front wings hook onto the frenum.
You pedal a trolley, which you hook onto the rails, and lift off when someone's coming in the other direction.
They hook onto a young player, the showier and more ballyhooed the better, and give him their hope and devotion.
The microtubules hook onto chromosomes at the center of the cell and are then retracted by the cell, pulling the attached chromosomes to either side.
I slipped the saucer's paper clip hook onto the wire, lifted my end of the wire to give the saucer a sliding start, and watched it fly!
I feel like in a weird way, he's also easier to hook onto because he's coming from the same point of view all the time".
Buy now 5. Eddington's Egg Poacher: £9.35, amazon.co.uk This retro-looking egg poacher is designed to hook onto the side of the pan.
In hindsight, did I need that charger that one could hook onto a car battery to power up a dead laptop?
Kiteboarders who use a harness to hook onto the fly lines can get dragged behind the kite if it malfunctions and the harness release mechanism fails.
The larger female essentially tows the male to shore, and sometimes a second, third and even fourth male will hook onto the line.
