40cm High Quality MDF batt, water resistant 6mm thick. Pre dilled for wheelheads with a 25.4cm or 10 inch centres wheelstuds. The second slot is cut elongated to accomadate slight differences in stud measurements. These batts will fit different sizes (i.e Rohde) 25cm to 26cm centre studs but will only be centred on a 25.4 cm centre.