Unfinished broad bolts are used to make broad-tipped bolts, the crossbow equivalent of broad arrows used to kill turoth and kurasks. They can be obtained from Slayer Masters, who will sell up to 3000 per day.
Provided the ability has been learned as a Slayer reward, they can be made into broad-tipped bolts using a Fletching skill of 55, giving 30 experience per 10 unfinished bolts. Unfinished broad bolts can be obtained by buying from a Slayer Master or from Jacquelyn Manslaughter. The stock for unfinished broad bolts are linked between all Slayer Masters except Turael/Spria, whose stock is linked to Jacquelyn's instead. To finish the bolts, add feathers to them.
Broad bolts require level 55 Slayer and 50 Ranged to be equipped, but they can only be fired from a rune or chaotic crossbow. They are commonly used for training the Ranged skill, due to their low price. They often substitute for more expensive runite bolts since both have 480 ranged damage.
Attempting to add feathers to make Broad-tipped bolts without learning how to make them gets the phrase "You need to learn how to make these missiles as a Slayer reward."
These bolts once had the damage of adamant bolts, but had their damage increased to 480, the same as runite bolts.