I got this thing from the package in which my prusa mendel was sent. The seller said he included spear part and I found some hardware, printed parts, and this thing. Can anybody tell me what is this? My guess is some kind of glue. Haven't try it out as glue yet.

it is likely fire cement.


the old days link below:
[reprap.org]

Makergear provide this with their older nichrome wire based hot ends.

They call it "Ceramic adhesive" but yes its basicaly a ceramic that can take the heat of a hot end.

see [www.makergear.com] for more info