Kotahi Grips from BJM Putting Science are designed for use with a "Runyan Style" hand position, with the arms rotated so the palms face the sky and the thumbs are on the sides of the grip instead of on top.  That position "locks" your arms to your shoulders, resulting in great stroke stability and accuracy.  
They come in two sizes:
Standard:100g, 14in length, 1.25in width, 1.75in height; Recomended for average to larger hands.
Undersized: 65g, 11in length, 1.125in width, 1.5in height; Recomended for smaller to average hands.
We supply Kotahi grips both as an option for Honu Putters and individually, for regripping your existing putter.