Calibrated Monofilament Pen The Retractable Monofilaments Pen are diagnostic devices that consist of a monofilament mounted in a hand unit for protection when not in use.The monofilaments are primarily used for testing the feet of diabetic patients for loss of protective sensation associated with peripheral neuropathy. If a patient cannot feel 10g, they should be considered at risk for developing pressure or neuropathic ulcers and should be referred to a specialist for further assessment. Supplied with full user instructions