Hi Doug,
A 1/4 inch carbide cutter (for aluminum) will make short work of those ridges.  That's how I removed them many years ago.

Ken Powell 501-847-4721

> On 08/08/2025 7:19 AM CDT DOUGLAS LOMHEIM dlomheim@aol.com <flyrotary@lancaironline.net> wrote:
>
>  
> I’m going to remove the shrouds around the spark plug holes, and was wondering what those who’ve already done, what method worked best?  With the price of “Mazda” plugs running $35 each, I’m going to replace mine with the NGK BR10EIXs…
>
> Doug
>
>
> Sent from my iPhone--
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub:   http://mail.lancaironline.net:81/lists/flyrotary/List.html