it's the same with wool, sinew, all kind of bar's (iron, steel, not silver, there is no large bar
Yeah anything that requires two of the same item works this way. It originally caused the game to crash and since they fixed that bug this issue has arisen.
Rope + Lid of Barrel = Shield
Hair + Hair = Thread
I had to start a new game to test this Spear thing out. At 0 level in crafting using a dagger on a branch had a "Not enough crafting" appear over character. Upon giving the items to a person with 1 in crafting I received a spear. Test with 0-3 in crafting. 1-3 created a spear of increasing power as craft level increased. Tested using the bloody dagger from Esmeralda as it was the first dagger I could find for a quick test.