The MakeMyBellyFit universal jacket extender is for expanding an existing jacket for pregnant folks. It includes fasteners that help keep the jacket zipper in place in the extender slide.

If you lost, broke, or never had (perhaps you got it used) the fasteners, this model is for you. I recommend printing 10 or so. You don't need one for every clip, but one for every 2-3 clips seems to hold pretty well.