KA
Worth 6 points before any premium square, and the 10th highest-scoring of 96 — tied with 1 other.
KA extends into 8 three-letter words, which is the 34th least extendable of 96 — tied with 7 others. That is the number worth memorising: a two-letter word is a place to put tiles, but a well-hooked one is a place to put them where the board stays open.
Every hook
- O→OKA
- S→SKA
- B→KAB
- E→KAE
- F→KAF
- S→KAS
- T→KAT
- Y→KAY
Not all of them are equally reachable, which a bare count of 8 hides. KA hooks on 7 distinct letters, and the ones you are likeliest to be holding are E (60% of opening racks), O (45% of opening racks) and T (36% of opening racks). The rarest is Y, at 14%.
How often you can actually play it
Out of an opening rack, 3.11% of the time you hold the letters for KA outright, the 15th least likely of 96 — tied with 2 others. Counting a blank as whichever letter is missing lifts that to 9.59%, though spending one of the two blanks on a two-letter word is rarely the play. Exact hypergeometrics over the 100-tile bag, not a simulation.
The only place a K goes
K appears in exactly one two-letter word, and this is it. If you are holding that tile and need two squares, KA is the whole of your options.