This a new genuine authentic Herman Miller replacement seat pan will only fit Mirra 1 Chair model numbers requiring a FIXED front seat indicated by an "F" in the 7th character space of the model number (i.e. MR112nFm or MR123aFm, etc.). Beginning Model numbers include ; MR111, MR112, MR113, MR121, MR122, MR123, MR131, MR132 & MR133 This Mirra 1 chair seat pan has an Airweave* seat suspension material that is lightweight and breathable and evenly distributes the user's weight over the seat of the chair. This seat options include a 17" fixed seat depth. If you have any questions prior to ordering, we will be happy to assist.