Set of 10 magnets Size completed ring: 18mm OD x 14mm ID x 30mm Long Material: Neodymium (NeFeB). Grade: N48 Coating: Nickel (Ni) SKU# MMOT181430 OD = Outer Diameter ID = Inner Diameter N48 equals very strong magnetic material that will produce their maximum strength up to 176 degrees F. Beyond 176, N48's begin to lose strength. ASSEMBLY REQUIRED: These magnets will be sent as 8 arc segments - 4 with N Poles on the outer diameter and 4 with N Poles on the inner diameter. PLEASE NOTE: As with ALL neodymium magnets, these arc segments are very fragile. Therefore, 2 extra arc segments will be included with each lot purchased - one of each polarity. *** Please be careful when assembling.***