This crown of thorns from Bethlehem is made from a small rose bush tree native to Jerusalem.    It has a double thorn pattern.  The thorns are approximately 1 inch long and very sharp.  The branches are harvested by Catholic monks and then shaped into the crown by a Christian family in Bethlehem.  Since this is the only thorn native to the Jerusalem area, it is likely that this is the type of crown that was placed upon Jesus's head.   The inside diameter is 7 inches.

Please note that these crowns of thorns are hand made,  not machine made.  Each branch is twisted and shaped individually and each is unique in shape and in placement of the thorns.  The crowns may indeed be more oval than round.  That is normal and not a defect.  Each is different and depends on the shape of the branch from which the crown is made.  The human head is actually more of an oval than a perfect circle.

Matthew 27:29

and then twisted together a crown of thorns and set it on his head. They put a staff in his right hand and knelt in front of him and mocked him. "Hail, king of the Jews!" they said.

(New International version)

Warning:  This is not a child's toy.  It is a replica of the Biblical crown of thorns and as such is very sharp.  Please be very careful when handling.