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| Patents for B43L 21 - Blackboard or slate-cleaning devices (5,409) |
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| 07/12/1983 | US4392268 Chalkboard eraser cleaner system | | 07/05/1983 | US4391013 Finishing tool for smoothing wallboard tape joints | | 06/17/1980 | US4207646 Chalkboard erasers | | 05/27/1980 | US4204298 Compact vacuum cleaner | | 07/31/1979 | CA1059272A1 Electronic way to rapidly erase a blackboard | | 08/08/1978 | US4104759 Custodial eraser | | 07/11/1978 | US4099286 Cleaners for chalk erasers | | 03/28/1978 | US4080683 Chalk board eraser | | 10/19/1976 | US3986224 Eraser with dust-collecting means |
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