This is a custom sized filter. As a result, these filters may not be returned for refund or credit. All custom size air filters are built to tolerances of + or - 1/8. This custom sized filter will ship within 2 business days. - fits generalaire power humidifier (drain type) models sl-16 series, 709 series, 990 series, 1040 series, 1042 series, and 1137 series. - measures approximately 9-3/4 x 12-1/4 x 1-1/2. - aluminum evaporator material is enclosed in heavy wire frame and channeling and has a super absorbent coating for maximum water distribution and increased humidity output. Excess coating may shake off before first use. - coated with a non-soluble wetting agent to increase humidifier efficiency. - for optimum performance, replace filter twice a season.