Replace the band and hinge

Take the old band off

Springs off first, dome open, helper holding it. The two hinge springs carry the dome's weight. Every Big Green Egg method takes them off with the dome fully open before any band or hinge nut is loosened (BGE UK). No BGE document warns about it, but owners report a dome whipping open, and one was hit in the face when a band slipped (owner report). The dome and base are heavy ceramic (52 kg together): work with two people. A dealer can do it for you, and BGE UK offers paid servicing.

BGE UK's Quadra-Link band how-to; the Mates step is from the Mates manual.

1. Open the dome and take both springs off.
2. Take the EGG Mates off: their brackets clamp round the lower band.
3. Undo the brackets and hinge (7/16 in).
4. Take out the 2 rear carriage bolts (1/2 in).
5. Lift the dome aside with two people onto a towel.
6. Take the old band off the base.

Fit the new band and set its height

BGE UK's method. No manual for the Medium's band kit (120021) was found: the kit steps are the Large's 2026 manual (117984), read for the Medium, with the 2020 Medium manual's counts.

1. Bolt the hinge brackets A to D to the new bands off the EGG (Large manual steps 1 and 2; the Medium manual uses 16 acorn nuts).
2. Fit the new band over the base with its holes lined up.
3. With your helper, set the dome back with its holes lined up.
4. Set the band height: the Large's manual clips 4 spacer tabs between the bands; the Medium's manual shows none, so use them only if your kit has them.
5. Tighten the rear bolts (1/2 in), then the hinge, then both brackets (7/16 in) (BGE UK).
6. Refit the springs, check for gaps, and re-check every nut after about 90 days (Medium manual step 9).