This is a replacement inner core for the Dremel Flex Shaft 225. Also compatible with the 232 model
Ends 2.64mm square
This is the same as the Dremel Part number 2610914543
See the link below on how to replace your old one
Sounds to me like the lubricant on the shaft might have overheated and solidified. Here is a previous response from Dremel. I got this reply from Dremel on the subject of a hot Flex-Shaft attachment. There will be some amount of heat present but nothing unbearable to the touch. Excessive heat is a product of either over or under lubrication, using the wrong type of lubrication or operating the flex-shaft with a sharp bend. Anyone of these will cause parts of the cable to overheat. The handpiece should be comfortable to hold in use and the flex shaft or spring around the flex-shaft should not overheat. The only piece that requires lubrication is the inner core of the flex-shaft.
To lubricate, unscrew the flex-shaft assembly from the motor housing. Pull the center core out of the flex-shaft shaft (it should come out very easily) and wipe it down with a dry rag. Wipe a very thin film of good quality, high temperature grease on the center core. We recommend our shaft lubricant #90952 or any type of good quality grease that does not break down under heat, such as automotive wheel bearing grease. The inner core requires lubrication after every 25-30 hours of use. Again, only a very thin (barely visible) coat of grease. Too much grease or using the wrong type of lubrication will cause the unit to overheat. Also, when too much lubrication is applied to the inner core it will run down to the handpiece causing overheating. This in effect will prematurely ruin the bearings. A small amount of grease is all that is needed.
The flex-shaft comes from the factory greased. As it settles there are areas on the inner cable that are heavily greased and other areas are not. When a flex-shaft is purchased from the store I recommend pulling the inner core out, put your hand in any kind of plastic bag and distribute grease evenly along entire length of cable. Slide inner cable back in the flex-shaft. Assemble the flex-shaft to the tool making sure that just the driver cap is on the motor shaft without a collet. Hang the unit and run on full speed under no load for 5-10 minutes. This will help distribute grease evenly.