Refill for Kokuyo Dotliner Tape Runner.
Each stamped rectangle is approximately 8.4 mm by 10 mm. A single 6.5-meter roll of adhesive tape can produce about 600 rectangles.
To replace the refill, push the tab at the top to slide off the front cover of the tape runner, then open the stamp guide. Swap out the spent refill for a new one, then reassemble the cover and stamp guide.
Dispenser sold separately here:
Kokuyo Dotliner Tape Runner (littlecraftplace.com)