In the game of contract bridge, Säffle Spade (or Säfflespader in Swedish) is a forcing pass-opening system developed by Einar Bergh and Pontus Svinhufvud; Säffle is a small city in Sweden where they once lived. There are at least three variants of the system: Super Säffle Spade (most advanced), Small Säffle Spade, and Small Happy Säffle Spade (simplest).
Treatment
While the opening bid of Pass is forcing for one round, it does not promise a very strong hand. The basic idea is that all hands (except certain pre-emptive ones) with 8 or more high card points (HCP) and 4+♠ are opened with a Pass (may also contain a longer side-suit). If one has 8 or more HCP and no ♠ suit, but 4 or more ♥, one opens 1♣ (may also contain a longer minor suit).
The general rationale is that when you open very low, you want to hold and show the major suits, so opponents cannot easily pre-empt against you. Another advantage is that when you have 8 or more HCP you often tell partner immediately which major suit(s) you do not have, and when he sees that your side cannot have any major-suit fit, if appropriate, he can quickly pre-empt with a minor-suit bid.
Today, the system is illegal in most competitions, since a "Pass" opening now may not be used to indicate strength. In the 1970/-80'ies when it was invented and actively played, such regulations were rare.