Corbin 27 Series keyways

X-Class. CO3, 1001EB/27-5. 1001EA/27-6. 1001E/27-7. Replaced 97 as Corbin's stock keyway. 27A1, 27A2, 27B1, 27B2 added later. 27 also enters Corbin 28 and 29 keyways. 27A1 was added in 1930, the rest added in 1963.