Alien I has two conventional springs.
Alien II has a four internal cam springs.
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↑ Set 206-208: CCH Aliens 3/8–3/4
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↑ 206: CCH Alien I 3/8: 11 mm.
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↑ 207: CCH Alien II 1/2: 16 mm.
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↑ 208: CCH Alien II 3/4: 21 mm.
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↑ 376: CCH Alien II 2: 49 mm.
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↑ 377: CCH Alien II 2 1/2: 59 mm.