Slightly bigger diameter of the base, ensures that the sides of the coffee puck is tamped well. It has a very snug fit with a 58mm portafilter basket. 
This professional coffee tamper has an ergonomic handle with the right design to 
pack the grounds evenly for a quality shot of espresso.  Artisan made.
 

Features:
Ash wood painted in black
Base is made of stainless steel 18/10 Aisi 304
Perfectly ergonomic for even pressing ground coffee to make espresso
Not suited for dishwashing
Flat Base
58.4mm