1) The name given to the wild apple.
1251 pomariis boscy, Snaith. The OED has ‘crab’ from c.1420 and ‘crab-tree’ from c.1425. In a boundary description for Ripon in 1481 was unum veridem balke [green balk] habentem in se duos crabtrees crescentes. Names provide earlier evidence: Crabtre was a locality in Bradford in 1355 and de Crabtre was a by-name in Sowerby near Halifax in 1388. The wood was being used by mill-wrights in the early sixteenth century for making ‘cogges and ronges’ and was recommended in 1742 for its ‘hardness and duration’. In fact crab-trees were grown in some spring woods and Sir Henry Cholmeley sowed ash chats & Crab cernells in 1653-4. The OED has 'crab-stick', a staff or cudgel made of wood from the crab-tree: 1616 'a case of assault with a crab-tree staffe', Thirsk.
2) Doubtless a type of ‘brake’, that is an implement for beating and crushing flax, possibly made of wood from the crab-tree, or an allusion to its claw-like shape, but the exact meaning is not clear.
1481 De uno brake pr crabbes cum hustillamentis ijd, York. The compound term is rare but occurs several times in the Selby area: 1669 3 stone of hemp, one crab brake, Brayton
1682 a crabbrake, a scile, a heckle, Brayton.