Lid, shelf and apex: the three gamma levels on a FlowMonkey board
Most gamma products call the heaviest call strike the call wall or the cap and the heaviest put strike the put wall or the floor. FlowMonkey uses lid, shelf and apex instead. The names changed because the measurements did: a 'floor' promises support, and when we graded the put side against a control it did not hold declines any better than a random level the same distance away. The words now say what the data supports.
The lid
The lid is the heaviest positive-gamma strike above price. Dealers who are long gamma there sell into strength, so a rally tends to slow or stall as it reaches it. It is a place price has trouble getting through, not a place it turns around.
Graded next session across 70,562 boards, the lid held about 84 percent of the time against about 74 percent for any level the same distance out. It is the one level on the board whose edge also shows up intraday, which is why the daily receipt grades it first.
The shelf
The shelf is the heaviest strike below price on the put side. Dealer hedging defends it first on the way down, so dips into it often get absorbed. We call it a shelf rather than a floor because the grading says it holds a little more often than a random level, not a lot: a real but thin edge, and price falls through it on plenty of sessions.
If a product tells you a put wall is a floor, ask to see the days it broke.
The apex
The apex is the single heaviest strike on the whole board, above or below price. Other products call it the king node or the magnet. We measured whether price is pulled toward it and found it is not: the apex is sticky, meaning price slows down when it gets there, but it does not attract price from a distance. Boards with a dominant apex actually reach it less often than any level the same distance away.
Since September 2026 the pre-open seal also records the apex of the 0-1 DTE book beside the all-expiry apex, because the two often differ and the near-dated one is what same-day traders are watching.
Checkpoint and clear air
A checkpoint is a level sitting between price and the lid or shelf: price has to clear it first, and the read says so. Clear air is a stretch with little gamma between price and the next level, where moves travel faster because there is nothing to absorb them. Both are descriptions of the map, not predictions.
Common questions
Is the lid the same as the call wall?
Yes, it is the same strike, the heaviest positive-gamma level above price. FlowMonkey renamed it because 'wall' and 'cap' overstate what the level does; it slows rallies more often than not, and the receipts show the sessions it did not.
Is the shelf a support level?
It is where dealer hedging is heaviest below price, which absorbs dips more often than a random level, but only slightly. Treat it as a place to pay attention, not as support you can lean on.
Does price get pulled to the apex?
Measured, no. Price slows at the apex when it arrives, but a heavy apex does not draw price toward it from a distance. Products that call it a magnet are describing a story, not a measurement.
Lid slows rallies and is the one level with a measured intraday edge; the shelf absorbs dips a little more often than chance; the apex is sticky, not magnetic. The names are chosen to promise only that.
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