A metal implant intended to be attached (sutured) to, or placed above, an arteriovenous fistula (AVF) under the skin to act as a guide when using a constant site (buttonhole) method of blunt needle insertion. It is typically used during haemodialysis procedures where the device can be palpated (felt) beneath the skin and the cannulation directed into the device where it will funnel the needle point towards a constant entry site in the vessel wall. It is typically made of titanium (Ti) and is available in a range of sizes.