Drum unit set is designed for use in Brother HL-3040CN, HL-3045CN, HL-3070CW, HL-3075CW, MFC-9010CN, MFC-9120CN, MFC-9125CN, MFC-9320CW and MFC-9325CW. The approximate yield is 15,000 A4 or letter-size, single-sided pages. Your printer will indicate when you need to replace them. The set includes four drums - one for each color: black, cyan, magenta and yellow.