If you mean a Hand Brush Brass is OK. Harbor Freight sells a 3 brush Set. Brass, Nylon and Stainless Steel Brushes somewhat the size of A Tooth Brush and also I think the sell larger individual Brushes that are Brass.

The only area that is sensative is the very tip of the Injector Nozzle and the Pintel.
It is not a good idea do brush the little Pintel nub sticking out with any sort of force and as I mentioned Hand Brushed only.

You can brush as much as want with a brass Brush on the interior parts and you can take a fine Stainless Steel wire Wheel or hand Brush to the exterior of the Injector but it can wear thorugh the Bluing and snag on the little return Nipples.

Please note that some purist would say no Meta Bruh at all should contact the end of the Injector Nozzle. That would only leave some sort of Plastic or Nylon bristle Brush with some sort of chemical to clean the tips.

Any sort of powered Metal Brush can scratch up the Pintle Numb and if the Pintle is pushed inside during the brushing can elongate the hole the Pintle sticks out of.

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