These branches are made from Grapevine Wood. This wood is safe for hamsters and a great enrichment to add to their enclosures. 
 
Each piece is a little different as these are naturally formed while growing. The pictures are some examples.
Grapevine branches can have some cracks formed naturally in the wood. If these are small you can cover with with moss and/or unscented tissue paper to help keep your hamsters from getting paws wedged in. We recommend this with any small gaps in general.