SFI Spec 3.3 Nomex Helmet Support / Neck BraceNZKW Australia SFI Spec 3. 3 Nomex Helmet Support Neck Brace Size: Large 17 inch This neck support collar fits around the drivers neck to take the weight of the helmet off the neck muscles, reducing fatigue. A hook and loop flap allows a small range of adjust ability, and the woven Nomex cover can be removed for cleaning. The resilient foam core can be shaved down to customize the fit if necessary. These collars are 360 degrees round.