What type of fastener is designed to be removed without leaving a trace except in the embedding medium?

The type of fastener designed to be removed without leaving a trace except in the embedding medium is a nail-in anchor. This type of anchor is specifically engineered for applications where minimal damage and a clean removal is desired. The design allows the fastener to be inserted into the substrate and secured without the need for permanent attachments.

When a nail-in anchor is removed, it typically leaves a small hole in the surface material, but the anchor itself can be pulled out easily without significant residual material. This characteristic makes it ideal for temporary installations or situations where the appearance of the substrate is important after removal.

Other types of anchors, such as drop-in anchors, toggle bolts, and machine screws, generally leave more significant marks or require drilling and could damage the surface more than a nail-in anchor does upon removal. Thus, the nail-in anchor stands out as the correct choice for applications requiring clean removability.