That is a Pentair Replacement Light Pilot Screw with Captive Gum Washer. Used with various Pentair pool lights such as the Amerquartz.
Pilot screw replacement
Fits Pentair IntelliBrite 5g Color and White LED pool lights
Also fits Pentair SAm Spectrum Amerlite, SAL Spectrum Aqualight, Amerlite and AmerQuartz pool/spa lights
Also compatible with Pentair Sta-Rite Sunbrite II and Sunglow II pool/spa lights
Made of stainless steel and includes captive gum washer; Measures 4-inch length by-inch height by 3-inch width
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pentair
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Light Parts/J-Box
IntelliBrite 5g Color LED Lights, After 2009 parts at Doheny's
Pentair 05601-0001 Stainless Steel Trim Face Ring
POOL360 30' Amerlite Light Spectrum 120V