Part II: Table Game Cheating · Dice & Craps Cheating Methods

Mercury Tappers / Tappers

How it works

Highly sophisticated loaded dice containing a dumbbell-shaped internal chamber filled with mercury (a dense liquid metal). When the die is resting normally, the mercury sits in the center chamber and the die appears and feels perfectly normal. However, when the player taps the die against the table before throwing, the mercury flows from the center to one end of the dumbbell chamber, shifting the weight distribution and making the opposite face more likely to land face up. Some variations use a ratcheting mechanism that holds the weight until tapped.

Where it appears

Private Games, Street Craps (obsolete in modern casinos)

On the record

One of the most sophisticated traditional loaded dice methods. The 1973 TV show “Police Story” featured a supervisor describing mercury-filled dice with “criss-crossed tunnels filled with mercury.” A veteran cheater confirmed these existed but noted they were “barely scratching the surface” of gaffing methods.

Published as a detection reference for surveillance, compliance and gaming-operations professionals. Thresholds and tuning are set by the property. Nothing here is instruction — the method is described so it can be recognised.