FN 509 Midsize Magazine Sleeve, 9mm 17 Round, Black. This FN America 509 Midsize Mag Sleeve is for the 9mm 17 round magazines. Made from durable polymer, this factory original sleeve can be placed on any compatible 509 17 round mag, allowing it to fit the Midsize models. This sleeve allows the use of a increased capacity magazine and extends the grip surface of the FN America 509 Midsize model pistols.#html-body [data-pb-style="62DF828A9FF7A"]{justify-content: flex-start; display: flex; flex-direction: column; background-position: left top; background-size: cover; background-repeat: no-repeat; background-attachment: scroll; border-style: none; border-width: 1px; border-radius: 0px; margin: 0px 0px 10px; padding: 10px;}#html-body [data-pb-style="62DF828A9FF86"]{border-style: none; border-width: 1px; border-radius: 0px; margin: 0px; padding: 0px;}