(38mm) OD neck to fit into a 1.5" shop vac hose. (Most "industrial/contract" shop vac setups use a 1.5" hose. .) It was a bit tricky 1, Finding 5" attachments and even more difficult making sure they actually fit my vacuum. This brush works well, appears to be of quality materials and construction and costs compared to others I've looked at, $10.
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