This Heathkit SB-220 & SB-200 Large Tuning Knob Insert Inlay, will fit the SB-220, SB-221, and SB-200 large tuning knobs.
For a perfect match it may be best to purchase this inlay for all three knobs.
It is very easy to install. You simply put a drop of contact cement in the middle of the back side of the insert and you can glue it on top of the old one, or you can remove the old scratched up insert with a pick.
To remove the old one you can drill a small hole in the middle area of the old insert to remove it with a sharp tool so you do not damage the edges of the inset area.It makes such a difference to replace the scratched or dinged insert as they are a focal point of attention.