ER-11 collets usually require:
- thin wrench for the flat on the shaft — usually 13mm, sometimes 12mm, 1/2" (12.7mm) is a good fit on some spindle shafts
- Powerbuilt Metric 6mm Combination Wrench, 12 Point Double Ended Box and Open End, 15 Degree Offset - 644110 - Amazon.com * Capri Tools 11850-1213 12 mm x 13 mm Super-Thin Open End Wrench, Metric - Amazon.com
- McMaster-Carr — note that these are currently: Product Information Martin 612MM Carbon Steel 12mm Opening 15 Degree Angle Check Nut Wrench, 101.59mm Overall Length, Industrial Black Finish - Open End Wrenches - Amazon.com
- traditional hex style ER-11 nuts require a 17mm open-end wrench — specialty ER-11 collet wrenches such as: ER11 Collet Wrench for ER11 Collet Nuts MariTool are available.