6mm od 5mm id thats the reason it has broke , a wall thickness of 1/2mm ??

decide which you want , 6mm od or 5mm id . will brass do ? thats the stuff sold by model shops / mode;l train shops / ebay , usually in about 12in lengh , I would go for 6 x 4 or somthing like that , but if you are adam ant on 6 x 5 , will stainless do , ebay

https://www.ebay.co.uk/itm/192736215338?_skw=6mm+od&itmmeta=01KS87GD06AZ3RYY3HESZ8K53A&hash=item2cdff9412a%3Ag%3AU74AAOSw96Zb7tUd&itmprp=enc%3AAQALAAAAwGfYFPkwiKCW4ZNSs2u11xDfvF3V0kKP2CE%2FjBhkTm8t9HIU9Og%2BIR1WuSeWDmWAWufirqIfIoAptEM%2FNzghjt9jrxYNF3%2FZi%2Fzzj001nGw3VgWC6HIZz6UE2bXuugz5PZ9twccD1%2BCvj%2FodmMrcEMUA0%2BUeEybmd0D8iVuM9S4G%2Fusmkt7RwV%2BE351M2XEAXE5RvR0mD1LfqglhtNorW51WHudeI4q22UGqp%2Be%2FbmfacVYLiUvxnX1YrCi4fmtStQ%3D%3D%7Ctkp%3ABk9SR8LQwYfKZw&var=496772381396