I use 2 flex shafts at a time when carving, one each for 3/32" bits and one for 1/8" bits. I get about 2 months of use before the inner core breaks. Then the flex shaft is no good...until now!! i found that i can order replecement cores right from Dremel. $4.90 each is alot better then 30 bucks for a whole new one. Here`s the phone number...1-800-437-3635. Ask for flex shaft innercores. I just ordered 3 cores for the 3 old flex shafts i have....now i`m stocked up and ready for another break.