Core size is usually decided by whatever the last supplier shipped. It sets your maximum roll diameter, your changeover frequency and whether the roll fits the mandrel at all.
A desktop printer takes a 40 mm core on a small spindle; an industrial applicator takes 76 mm on a 3-inch mandrel. There is no adapter that makes a 76 mm roll run well on a 40 mm spindle. Check the machine before the quote, not after the delivery.
The same label count needs a much larger outside diameter on a 40 mm core, because the winding density near the core is poor. On a tight line, that means either more changeovers or a roll that will not fit the unwind.
A 40 mm core turns faster at the same linear speed, so the unwind has to hold tension over a wider range. On high-speed applicators this shows up as registration drift at the end of the roll, which is often misdiagnosed as a die problem.
For high-volume automated lines, coreless rolls remove the changeover entirely and cut waste at the end of the roll. The trade-off is that they need a dedicated unwind — they will not run on a standard mandrel.
40 mm and 76 mm as standard, cardboard or plastic, and coreless on request. Tell us the machine model and we confirm the core, the maximum outside diameter and the wind direction in the same reply as the price.