The same as the D4 whetstone, but instead of the leather pouch, it is sold with a double coated pressure sensitive adhesive tape which allows you to fasten it on any flat spot, e g sheaths. The VHB 5925F tape is extremely strong and will harden permanently within 24 hrs. In size the D3t will fit the F1, H1 and S1 zytel sheaths, while the D4t fits the A1 zytel sheath. They will also fit some non Fallkniven sheaths and other products.