When I first purchased my cello Adam mentioned that my endpin was bent. I thought this was a fairly cheap upgrade, so I purchased a New Harmony carbon fiber endpin for $45 at Everything Cello.
I purchased an 8 mm endpin without a fitting option because the website stated it "fit most standard fittings." However, once I received the endpin, it wouldn't slide inside my existing fitting past 1/2 inch.
Luckily, my husband knew what to do! We headed off to Home Depot and purchased fine sandpaper and graphite lubing. Normally, the graphite tubing comes in a small tube, but Home Depot only had the large canister.
My husband sanded down the fiber carbon endpin, wiped off the excess shavings and it slid right into the fitting.
Word of advice: Put on gloves and lay down a garbage bag or something to cover the table. Sanding down the fiber carbon gets messy! And use a mask too.
My happy cello with its new endpin! :)
The New Harmony endpin is a lot lighter than my old steel endpin.