All arm-sizes can be fitted with a Knockstop ®. A tie wrap, with a rubber hose as a liner is used to secure the elbow of the user in the holder. The correct position for the rubber hose is near the inner side of the elbow. See the figures below.
For more safety preferably two holders on both elbows must be used. This product can be purchased on the reknown 3D printing and lasercutting website, www.ponoko.com: