Brother and AllBrands recommends changing both knifes at the same time to avoid the new knife blade from getting damaged or prematurely worn by cutting against the older blade

For Brother 925D 929D 935D 1034D, 3034D, PL1500-1600-2000
Nancy G, Antelope CA
I'm a long-time customer of Allbrands and find them a trusted company with a very large selection of sewing and pressing items.