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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 maximal 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:

Use a long tie wrap in a rubber hose to secure each holder to the elbow.

Putting on the Knockstop® is easily  and quickly done by extending the tie wrap and then inserting the arm:


Knockstop®: The friendly prevention of aggression. Article: Violence in the nursing home Article: When aggression follows dementia
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