You sure it's not just some sort of cap that slips out? Or force it in I guess. Manufacture may add that to keep out moisture. All the end set ups come like this unless you are buying for a stock handlebar. I have protapers, just hollow tube.

CICMOD Universal Motorcycle Street Bike 7/8" Handlebar Grips Bar End Plugs (Black) for Kawasaki Suzuki Yamaha Ducati Triuph https://www.amazon.com/dp/B016MFA51U/ref=cm_sw_r_apan_i_KNPK65S45W6Q1E8KKPQY