These are Replacement M6 Stainless Steel T-nuts for the any hydrofoil that uses the M6 T-nut including Takuma, Naish and others  These are hard to get replacements that we now have in stock.  They are sold each so if you need a set of 4 make sure to buy 4 of them.  Watch the video below for our testing of the M8 version against the brass version. 

Here are the total dimensions of this part: 

Track width: 8.5mm
Total width: 14.9mm
Total length: 23.9mm
Total height: 6.20mm