This item is used in the Trueshot Longbow quest.
The quest, as written up on Alla, states:
"Maesyn Trueshot says 'Take this pack. Go to Kaladim, find Trantor Everhot and ask for dwarven wire. Then go to Freeport to meet Jyle Windshot. Search the inns for him and ask him for treant wood. Then, collect some spiderling silk from spiderlings and finally, in Steamfont, we have the permission of the gnomes to use any micro servos we find while destroying rogue spiders. Combine them all and return the pack to me.'
You receive a Trueshot Assembly Kit, a 10-slot LARGE container."
You do not receive the assembly kit (that item is used for wood elf ranger newbie armor quests. Instead, Maesyn gives you a Material Pack.
Scruetayp, 78 Leezard Necromancer of Quellious
Ryllian, 65 HERC of Quellious (reliving the glory days of quests)