100-Pack Purple 18mm Double Square Aluminum Nipples for Plumbing, DIY Projects & Home Repairs - Durable Pipe Fittings for Water Supply & Gas Lines

The Double 4-Kant (double square) head allows for tensioning of the spoke from either side of the rim, a big advantage over traditional nipples is that the wheel can be built without the visible surface of the nipple being damaged, they also allow for better align with the spoke and helps prevent excessive buckling of the spoke while lacing. This head style adds 4mm to the overall nipple length, so an 18mm nipple has an effective length of 14mm and the 16mm has an effective length of 12mm. These nipples are designed to help with centring, and can be used for hand lacing. The overall length of the nipple is 4mm longer than the effective (usable) length.