Several common adhesives function very well on many forms of rigid plastic, including two-part epoxy and immediate glue (cyanoacrylate). In addition there are two-part acrylic glues made merely for gluing plastic, including Loctite Epoxy Plastic Bonder and Super Glue Plastic Fusion, but neither are advocated for pasting polypropylene and polyethylene plastic.
Another option is a two-part immediate glue, Loctite Plastics Bonding System, that’s designed to function with most all plastics, including polypropylene and polyethylene.
Age or some adhesives dry to a light yellow color, so be sure to have a great fit between the bits and wipe off any surplus. Hold the bits in place until into the glue sets, or use spring clamps, clothes pins, rubber bands, or modeling clay to hold the parts before the adhesive dries.