Title: Frangible construction lock system

Abstract: A pin tumbler lock has a housing, a cylindrical key plug provided with a keyway rotatable in the housing, a shear line between the plug and the housing, pin tumbler bores with aligned parts respectively in the housing and the key plug and spring pressed outer and inner pin tumblers in each bore. In one of the bores is an extra frangible graphite tumbler of substantially the diameter of the other pin tumblers. When construction key is inserted in the keyway the graphite tumbler and the other pin tumblers meets at the shear line permitting the lock to unlock. When construction is finished a conversion key is inserted in the keyway and the graphite tumbler is shifted to a position crossing the shear line whereupon the graphite tumbler is shattered by rotation of the key plug. Thereafter the lock can not be unlocked by the construction key but can be unlocked by the householder's key.

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Inventors: Fane, William J. (North Vancouver, CA, US)

Application Number: 573067
Filing Date: 1975-04-30
Publication_date: 1976-12-21
Assignee: Norris Industries, Inc. (South Gate, CA)
Primary Class(es): 70/338 70/340, 70/384, 70/493
Other Classes:
US Patent Ref:

564029	Jul, 1896	Sargent	70/364.
3070987	Jan, 1963	Baker et al.	70/338.
3095726	Jul, 1963	Schlage	70/383.
3149486	Sep, 1964	Russell et al.	70/384.
3172284	Mar, 1965	Crandell et al.	70/383.
3175379	Mar, 1965	Russell et al.	70/384.
3190093	Jun, 1965	Schlage	70/383.
3234768	Feb, 1966	Russell et al.	70/338.
3315503	Apr, 1967	Schlage	70/383.
3563071	Feb, 1971	Barger	70/378.

Other Refs:
Primary Examiner: Gilliam, Paul R.
Assistant Examiner: Calvert, A. M.
Attorney: