1" vapor barrier christmas tree fasteners for crawlspace moisture barrier poly liners, covers and encapsulations - parts & accessories (white, 100 pack) elk elk vapor barrier fasteners are used for mounting and securing a plastic moisture barrier to the foundation walls and pillars in the crawl space. vapor barrier fasteners are approximately 1 inch long. actual dimensions are 22.7mm in length by 7.5mm in width with the diameter of the cap measuring 18mm. to install, drill a hole, using a 1/4" masonry bit or smaller, into the wall and then attach wall liner with christmas tree fastener. to seam and seal your moisture barrier, consider using butyl tape or vapor barrier tape. and for that finished look, consider using capped vapor barrier stakes. these will secure the moisture barrier poly liner to the ground. all said and done, you'll have one professional looking crawl space encapsulation.