Amazon.com : PM501 Manfrotto Type Quick Release Plate with Arca Swiss Type Clamp Built in Compatible with 501PL / RC3 / RC5 / NG Heads Features ProMediaGear Strap Port, for Video Heads
Manfrotto-Type QR Plate with Arca-Swiss Type Clamp Built-in For 501PL / 502 / 504 / Nitro / RC3 / RC5 / NG Heads – ProMediaGear
Amazon.com : Fotga Rapid Camera Quick Release Sliding Plate 501PL Replacement with 1/4" and 3/8" Mounting Screws for Manfrotto 501HDV 503HDV 701HDV MH055M0-Q5 Ball Head : Electronics
Compatibility between Manfrotto 501PL and 500PLONG with quick release system 577 and MVH500AH - YouTube
SmallRig Manfrotto-Style Aluminum Drop-In Base Plate for Manfrotto 501 – JG Superstore