What I do is thread it normally.
Then turn the die around and thread it all the way.
This will make it have full threads all the way.
Normally you will have tapered threads. This is due to the nature of the die.
By turning the die around you cut the deeper threads the full length instead of half.
Yeah I would buy a tat. For a slant brake is it not as critical. But when you install a longer brake, like a 74 style then you risk the chance of the bullet hitting the end of the brake if you don't use a TAT. This is caused by the threads being crooked. In 93 I threaded a MAK90. I was pretty lucky. My threads were not perfect, but pretty close. After I went to the range and blasted a couple mags I came back home and cleaned the gun. I had a 74 style chinese brake on it. At the very end of it, on the inside there was some copper. The bullet appearently sideswiped the inside edge of the end of the brake. Not enough to cause damage but enough to leave marks.
I now use a TAT. You can "rent" a threading die from WJM on gunsnet, but I would recommend that you just buy one. they are not that expensive.