 I've gone to thicker wall tubing. It allows use of a regular socket to service the bolts. Tubes and Castellations can be made different lengths per customer wishes, to suit different brand hubs.
|  Pic as if on a truck. This hub is my only loose sample. Other brands may need different component lengths to protect knobs.
With this tube length, the OE Warn style lock tabs should work. Or I believe a generic lock for 7/16" bolts should too- if we can find those either. Or drill the bolt heads for safety wire?
|  Alternative design: Without castellations. Note that bolt heads will ultimately be acting as the protectors. I suppose other brands of hubs migth need a longer protector? Or may need the castellations because the shorter bolt sleeves would allow more room for gripping the big knobs on the end of the hub?
|  Off the hub. The 3/4" diameter sleeves will support the bolts, and the 'walls' will tie the sleeves together, so any load will be spread between multiple bolts.
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