Mezz only does 3 joints: United (Modified 5/16x14, Wavy (Modified 3/8x9) and Standard 5/16x14 piloted (WxH 12.10mm x 4.10mm). The first 2 only fits a Mezz Butt. They don't offer blanks still even if many are asking for it. I don't think any Mezz dealer carries the 5/16x14, but you can try asking J&J.