This is a spinner cylinder head cover specially manufactured by Kitaco Co. in Osaka, Japan.
It fits Honda Monkey 125 and MSX 125 Grom engines.
Easy to install on engine fittings.
Here are several technical informations from manufacturer:
FOR DRESS-UP CYLINDER HEAD.
BEARING IN THE TOP PLATE TO TURN FOR UNIQUE ACCESSORY.
※IT DOES NOT HAVE TO DO WITH CAMSHAFT REVOLUTION.
※SIDE COVER IS EXTREMELY HOT WHEN ENGINE IS ON. DO NOT TOUCH WHEN IT IS HOT.
○TOP PLATE / BASE PLATE : ALUMINUM MACHINED
○DISC : ALUMINUM