After a 4th best lead, the partner of the opening leader can use the Rule of 11 to place cards in declarer's hand. The rule works as follows:
- Subtract the denomination of the 4th best lead from 11.
- This tells you how many cards higher than the led card are in the other 3 hands (declarer, dummy, and the leader's partner)
- You can see how many cards dummy has which are higher than the opening lead
- The partner of the leader can see how many cards they have which are higher than the opening lead
- Add your higher cards and dummy's higher cards
- Subtract that total from 11 - the denomination of the opening lead
- That is how may cards declarer has which our higher than your partner's 4th best lead
Declarer can use the same rule to determine how many cards the partner of the leader has which are higher than the card led.
Here is a 57 second video on the Rule of 11.