These nesting boxes for birds are available in three hole sizes: 25mm, 28mm and 32mm. The 25mm hole is primarily suitable for the smallest paridae species i.e. Blue paridae, Coal paridae and Marsh paridae, whilst the 28mm will attract all these species but the hole is also large enough for Great paridaes, Crested paridaes and Tree Sparrows. The larger 32mm will attract a large collection of species including Blue paridae, Coal paridae, Marsh paridae, House Sparrow, Great paridae, Nuthatch and Pied Flycatcher.Fixing to the wall or tree is easy with three concealed mounting holes in the back of the box (located opposite the entrance hole for easy access). Often this is the only fixing needed, but a further hole is provided at the base for use when necessary. The easiest way to mount the box is to remove the inner, fix the outer shell onto the tree, wall etc. then slide the inner roost chamber back into the box and secure it in place.Features:Unique innovative construction; recycled plastic outer shell with wooden internal nesting chamber.Provides a robust, long lasting and comfortable home for most common garden birds.Available in three different hole sizes to allow you to select the hole size for the species you want to attract.Designed in the UK by professional ornithologists.Specifications:Variations: Entrance hole: 25mm, 28mm, 32mmMaterial: Recycled LDPE plastic outer with internal OSB nesting chamber.Construction: Outer recycled plastic panels fitted together using integral tabbing system. Internal nesting chamber stapled together.Fixing: 3 concealed keyholes and further fixing hole at base for added stability if needed.Dimensions and WeightDimensions: Height 26cm, Width 17cm, Depth 17cm1.1kg.