These birch logs are natural so each piece may vary a little on appearance. Some may be a little thicker than others as shown on picture. 
Length 20cm
Entry hole 6.50cm
Side hole 7x6.50cm
Material: natural birch wood log. Pet grade, free of pesticides and chemical treatments. 
If you are using them for hamsters we recommend freezing these for 48h+ defrost 24h & refreeze 48h+. These natural birch logs have a very thin flaky bark so may not be suitable for your oven.