square key;

acquired with kind help of Mr Valčić, owner of VALCIC DRUMSTICKS; hvala, Lorenzo

From their website:

Valcic drumsticks are made of first-class American hickory, which does not crack even with the strongest blows! The feel of these sticks in the hands is ideal for quick changes to drumming elements, and the shape of the tip of the stick guarantees the best sound on cymbals. So everything a drummer needs!