The collar attached to the collar prevents the wounds from being licked or scratched, e.g. injuries in the head area. If necessary, the edge of the collar can be protected with tape, so that it does not rattle so loudly, e.g. when it hits the wall.
If the need for a collar is known in advance, it is worth getting used to it well in advance, e.g. with treats and praise.
Size - neck circumference/height of plastic part
XS - 22-25cm/7cm
XS/S - 22-25cm/10cm
S - 28-33cm/12cm
S/M - 31-38cm/15cm
M - 38-44cm/20cm
W - 44-50cm/25cm
L/XL - 47-57cm/30cm