This is a 3/8-16 Tap to fix stripped t-nuts.
How to use
1. Spray some cutting fluid, WD40, or other oil to aid in cutting.
2. Hold the tap in line with the t-nut and turn it clockwise. Try to keep it very straight as you turn; this is important.
3. Every few turns, back the tap out (counterclockwise) to clear away chips of loose material.
4. When the tap has passed through the t-nut, back it out, clean out chips and any cutting fluid or lubricant, and try a bolt with your hand first.