101532 IKEA BILLY SHELF SUPPORTS PINS FIXINGS PEGS METOD UTRUSTA original spares | eBay
IKEA Billy bookcase tip: if you have an OLD Billy bookcase (pre-2014) you can still add extra shelves even though the new extra shelves from IKEA use a new, disc-shaped shelf pin.
ReplacementScrews Shelf Support Pins/Pegs Compatible with IKEA Part 101532 (Pack of 5) : Tools & Home Improvement - Amazon.com
IKEA BILLY UTRUSTA METOD SUPPORT PINS 101532 BRAND NEW ORIGINAL PARTS X12 | eBay
101532 IKEA BILLY SHELF SUPPORTS PINS FIXINGS PEGS METOD UTRUSTA original spares | eBay
12 PCS IKEA BOOKCASE SHELF PINS 101532 Parts cabinet Peg Support Utrusta Gersby $9.99 - PicClick