Thumb up thin hand technique

Trying to get this jam figured out. Anyone got advice/ post pictures pulling it off?

The way I’m working it feels like it won’t work as a a straight in jam

Looks like Kent's crack climber's manual.

For straight in jamming, personally if I can't get past the knuckles at the base of my fingers and actually into the hand itself, I pretty much always use finger stacks and ring locks. I do use that technique as the lower hand in corners and use the thumb to kind of hook the edge of the crack as long as there is an edge to hook. hooking the thumb suchly only works with the arm more to the side than reaching high and helps pull the body into the corner. I kind of consider that more off fingers than hand size though.

Edit, come to think of it, the pic may be slightly misleading in that the edge of the crack is shown on the fingers/knuckles, but not the back of the hand. Yes, I do use that technique with thin hands. The technique overlaps with standard hand jamming dropping the thumb across the palm, but it's a matter of degree how much meat you can get in the thinner than Ideal hand size crack.

And BTW, personally I avoid thumbs down whenever possible. It is harder anatomically, and limits movement per reach/move. While thumbs down can feel more secure, with practice thumbs up is more efficient. Except in corners. Then typically thumbs facing eachother and shuffle upper hand leads, lower hand follows.

Does this help?

Thin hands is a challenging size. That jam will work best when used with the low hand. Above eye level and you'll probably want to switch to a thumb down jam. Basically, shove as much of the meat of your hand as you can into the crack and cup fingers hard.

Its hard to explain, think of it like you are trying to bring your thumb beside your index finger instead of on top of it, while pressing your fingertips into the wall. You are trying to fill the space between the base of your index finger and the wall of the crack with as much thumb as you can.  Similar action to a normal hand jam
But the camming action is taking place at your thumb knuckle instead of the base "meat"

Yes it's Kent's book.  Link https://www.fixedpin.com/products/the-crack-climbers-technique-manual

@moutainhick, your post is very helpful.  I agree completely on the thumbs down.  I used it a lot when I was learning to jam, but rarely use it now a days unless it's a corner, or an off situation.  Your description follows my experience.  There is a crack that keeps spitting me off in the transition from bomber locks to desperately tight/edge of thin hands.  I've also found it is usually easier to just keep pulling on stacks then switch.  I end up camming my individual knuckles on top of one another (between a lock and donut jam), and that's helped but it still feels super desperate at the transition from locks to hand jams.  I was hoping this might be a new trick.  If I can get it strong with my lower hand then it may give me the extra security I need to pull into the hand jam.  Your picture helps a bunch.  The one in the book shows the knuckles out so far that it left me with a what-the-hell head scratch after several attempts on a crack machine.