Need the Googleable name of a thing to I can buy some

Edit: SO I can find some. Goddamn phone keyboards.

I need some nuts like bicycles use for seat posts and axles that have a lever to quick-release or tighten them. I need them in a larger size though.

Allow me to 'esplain... I made a sliding cargo keeper for the bed of my truck. It uses the rail system that was there. That rail accepts a T-Slot nut or the head of a bolt. So, my plan here was to use the head of a 7/8 bolt in the rail, thru a flange on my "wall", thru a spring and into one of these nuts so I could easily move/adjust it and clamp it with one hand to keep things like gas cylinders and fuel jugs from sliding around when I need to.

All I can find are bicycle axle sets and wee little metric ones.

They're called hub quick releases, and sometimes 'skewers.' I've never seen the lever mechanism in larger sizes myself though.

They are just called quick releases: https://www.amazon.com/s/?ie=UTF8&keywords=bike+front+wheel+quick+release&tag=googhydr-20&index=aps&hvadid=178138706553&hvpos=1t1&hvnetw=g&hvrand=17855201744322847656&hvpone=&hvptwo=&hvqmt=b&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021544&hvtargid=kwd-14779244862&ref=pd_sl_3ytt520hz0_b

But if I understand what you're wanting to do, it won't work anyway, as the lever part is usually attached to axle.

Cam Lever?

https://www.grainger.com/product/32PJ59&AL!2966!3!166587749707!!!g!71846390359!?gclid=CLrDssj56tMCFQEEaQodFj0Aqg&s_kwcid=AL!2966!3!166587749707!!!g!71846390359!&ef_id=WBN3rQAABXv8ZCyv:20170512180852:s