Bomb at Town Hall 10: 6 of them, max level 7. At Town Hall 18 the cap is level 14. Max level per Town Hall, with how many you can build in brackets: TH3 2 (2), TH4 2 (2), TH5 3 (4), TH6 3 (4), TH7 4 (6), TH8 5 (6), TH9 6 (6), TH10 7 (6), TH11 8 (6), TH12 8 (6), TH13 9 (7), TH14 10 (8), TH15 11 (8), TH16 12 (8), TH17 13 (8), TH18 14 (8).
Tap a Town Hall to open this item there. Dashed: not available at that Town Hall yet.