Thread

Thread is used along with a needle to make armour out of leather, dragon leather, and cured yak-hide. It can be bought Thessalia's Fine Clothes in Varrock or in crafting stores, such as the one in Al Kharid. For yak-hide users in Neitiznot, thread can be bought from Jofridr Mordstatter in the bank on the island. Each thread spool has 4-5 uses before its supply of thread runs out and it is consumed. Getting five uses out of one spool is rarer than getting four uses. They are stackable, so many may be carried at once for larger-scale crafting.

A spool of thread is also a loot from baby impling.

There is a spawn point in the Jolly Boar Inn, located north-east of Varrock proper.

Trivia

 * Though 4 uses per spool thread is VERY common, some players have indeed received 5 uses per spool, which is uncommon, but not unheard of.
 * Depending on your level, it is possible to consistently get 5 uses. A level 28 Craftsman has gotten 100 uses out of 20 spools (5 each) making Leather Hardbodies.