MASTERCARVER REPLACEMENT INNER SHAFT
Flexible shafts are designed in such a way that if the shaft is over- stressed i.e. rotating accessory stuck in shirt, that the shaft will break at a fitting (either end of shaft) providing a measure of safety to prevent injury to user or motor. Typically the shafts and sheaths are replaced a number of times throughout the life of the tool.
To prevent premature shaft breakage, do not bend shaft more than 90 degrees or jam accessories into work, never put accessories to work unless motor shaft is rotating.
If using reciprocating handpiece, make sure tools are sharp, use minimal pressure, before use, make sure end of shaft extends past the outer shaft fitting not more than 3/4" (see "Replacing Flexible Shafts & Sheaths" for details). Remember shafts can break at any time if overstressed, so we advise keeping a spare shaft on hand.
REPLACING & ADJUSTING FLEXIBLE SHAFTS & SHEATHS
Replace shafts & sheaths immediately if worn or broken or if metal fittings are loose. To remove shaft & sheath, follow the following steps:
1. Turn off motor and unplug from outlet.
2. Remove the handpiece by griping the metal fitting at the end of the black flexible shaft with one hand while griping the handpiece with the other hand and pull apart sharply.
3. Loosen set screw from knurled nut at motor base.
4. Slide off sheath (hose assembly). 
5. Remove knurled nut at motor base (this has a left hand thread and must be turned to the right to remove).
6. Loosen set screw on flexible shaft coupler at motor and remove coupler.
7. Apply a small amount of shaft grease (789001 Pro Flex-Shaft Lube) to the entire length of a new flexible shaft. Note: Lab results prove that this exclusive synthetic lube is best and unlike others is only needed once in the life of the shaft.
8. Reverse the procedure for removing flexible shaft and sheath.
9. Measure length of the end of shaft, to confirm that when held straight it extends past the outer shaft fitting at least 1/2" but not more than 3/4". If necessary, adjust the exposed shaft to the proper length by loosening the set screw on knurled nut at motor base and / or set screw on shaft coupling and adjust as necessary for proper length.