Stiff Thumb is one which does not bend backwards like the supple thumb but remains stiff against any pressure to bend it backwards. Usually it tends to remain close to the hand. The individual with stiff thing to the test of his common-sense. He is cautious, determined. He plods along, does not spend lavishly and neither gives confidence nor invites but a steady person who does not attempt many things at a time rather successfully completes a few attempted. He has the sense of justice and great self control. The quality of skin consistency and color certainly make a large difference in qualities of this thumb. The coarse skin would make the possessor of stiff thumb stingy and hard hearted while fine skin will produce economy and sense of justice.
Generally there is brutal force behind the will of this thumb. If the second phalange is also developed and thick the arguments and reasoning are blunt and the person is too out spoken.
The consistency tells whether constructive energy or laziness is directing the will and logic. A weak thumb with energy is better than a good thumb spoiled by laziness of flabby consistency. Good thumb on a soft hand would like to exert itself but will get tired too early.