Arrow Fastener #506 T50 3/8 in. W x 3/8 in. L Flat Crown Heavy Duty Staples 1250 pk. Pack of 10, Packaging may vary. STAPLE 3/8" T-50 1250PK T50 staples are the world's best-selling heavy duty staple platform. Made to deliver exceptional holding power, these staples are used for all heavy duty stapling applications from installing insulation, house wraps and roofing underlayments to upholstering fine furniture and window treatments.