Spiral arm spurs were analyzed on B and I photographs of NGC 628, NGC 2403, NGC 3031, NGC 4321, NGC 5194, NGC 5236, and NGC 5457. The inclination-corrected pitch angles, lengths, and widths of the spurs, and separations between adjacent parallel spurs, were measured. Time scales for significant shearing of the spurs due to differential rotation and to spiral density waves were determined from published rotation curves. Spurs appear to be long-lived features with pitch angles of about 60 deg and widths of some 560 pc.
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D. M. Elmegreen (1980) studied this question.