The difference between the 1/2″ and 3/8″ diameter tubes is just a bit over 1/8″ in diameter. This translates into the following differences when chewing (these are generalizations as all chewers are unique):
-1/2″ tubes are a bit more robust (hold their shape longer) for older, stronger chewers (over age 12, but there are exceptions)
-3/8″ tubes are for younger chewers and feel softer when chewed (though the hardness- durometer- is the same between the two tubes)
-Alternatively, 1/2″ tubes feel harder when chewed
-It has been reported by some chewers that the 3/8″ tube creates or collects less saliva when chewing than the 1/2″ tube
Deciding between the 1/2″ and 3/8″ diameters depends on how strong your chewer is and their preferences. If in doubt, start out with the 3/8″ tube and move up to the 1/2″ tube if it appears that your chewer needs just a bit more hardness or durability or just prefers the larger tube size.