Newbie here ..63 yr Mamaw and resident mechanic lol

[mamaw dawn]

Just bought my grandson a silver fox ..trying to replace front wheels /tires ...I know this is a simple answer ..but .....is it 15mm or 17 mm ?? Please be gentle here ..yes I tinker around the garage and am trying to explain things to my 13 year old grandson (I am raising by myself). I ordered some front wheels from Amazon ..only to realize I need the hub ?? It take 3 bolts .. where as the original was a one piece .. not sure if I should just return these or upgrade ..it is an older kart but is budget friendly for me ..lol ..any help?? Thank you very much Mamaw Dawn