A steppingstone squeeze occurs when a defender is reduced to giving declarer an entry to an otherwise inaccessible winner. It is a type of strip-squeeze originally described by Terence Reese in "Master Play in Contract Bridge" in 1960. (The other two that Reese presented were the vice squeeze and the winkle.)
To illustrate:
North
♠ J 2
♥ —
West
♦ 3
East
♠ 9 8
♣ 6
♠ 7
♥ —
♥ 5
♦ Q 4
South
♦ —
♣ —
♠ —
♣ 7
♥ Q
♦ K 8
♣ 2
South is on lead needing 3 tricks. He only has 2 winners in hand — the ♥ Q and ♦ K — and no way to reach the good ♠ J in dummy.
If South plays the ♥ Q, though, West will be squeezed. To protect the ♦ Q, West might decide to discard a spade. In that case South continues with the ♦ K and the ♦ 8. West, thrown in, must ignominiously lead a spade to dummy's jack.
The steppingstone squeeze is so named because declarer uses a defender as a surrogate entry, or step, into the other hand.
Example
The following deal was authored by the late writer Alan Truscott (1925 - 2005) for The New York Times.1 South landed in a 1NT contract and received an opening lead of the ♠ 4:
North
♠ A J 7
♥ J 6 4 2
West
♦ 10 8 7 4
East
♠ 4 3 2
♣ J 6
♠ 10 9 8
♥ A 8
♥ 9 7 5 3
♦ Q J 5 3
South
♦ A 6
♣ A K 9 8
♠ K Q 6 5
♣ Q 5 4 2
♥ K Q 10
♦ K 9 2
♣ 10 7 3
"As it turned out, a minor suit lead would have defeated the contract, but West tried a spade in the hope of finding a spade suit in his partner’s hand. The declarer won with the ♠ A in dummy and led a heart to his king. West won with the ace and shifted to clubs. After four rounds of the suit, West was on lead in this position:
North
♠ J 7
♥ J 6 4
West
♦ 10 8
East
♠ 3 2
♣ —
♠ 10 9
♥ 8
♥ 9 7 5
♦ Q J 5 3
South
♦ A 6
♣ —
♠ K Q 6
♣ —
♥ Q 10
♦ K 9
♣ —
"West continued with a spade, the only play to give South a problem. This severed the North-South communications, making it impossible to cash six winners in the major suits. However he plays, South finds himself cut off from either the ♥ J or his own fourth spade trick.
"South did not choose to stake everything on the position of the ♦ A, so he cashed his three spade tricks, throwing a diamond from dummy. East became the victim of a ‘steppingstone squeeze,’ a rare ending. In order to keep his three hearts, and prevent South from overtaking the ten with the jack in dummy effectively, East had to throw the ♦ 6. South cashed his queen and ten of hearts, noting the discard from West at the 11th trick.
"The declarer had to lead from his ♦ K at the 12th trick, but East had to take the ace and give dummy the last trick with the ♥ J."
References
1Truscott, A. (1968, December 5). Solodar and Bethe Form Pair at Last Minute and Win Title. The New York Times.
See also
Vice Squeeze
A squeeze that operates against a defender's doubleton of touching rank, e.g. Q-J.