Check the listing for details. Fiber Optical Tool, 20 Pack 5mm/7mm Ceramic Core for Visual Fault Locator. Condition: New. Listed at 11.85 USD. These fiber sleeve core spare ceramic inserts are designed for versatile use. They are suitable for most fiber cable testers and red light pens, making them an essential accessory for fiber optic testing and maintenance.Specification:Material: CeramicTotal Size: 5 x 3.6mm / 0.2 x 0.14"(L*D), 7 x 3.6mm / 0.28 x 0.14"(L*D)Package Content: 10 x 5mm Ceramic Core, 10 x 7mm Ceramic CoreAdvantage:Made from quality materials, these inserts are highly durable and resistant to breakage. They ensure a reliable and extended lifespan, allowing for consistent performance during fiber optic operations.Instruction:With improved design and construction, these inserts provide easier installation compared to traditional options. This simplifies the replacement process and reduces the risk of damage or improper connections.