These speaker spike / isolation pads are SOLID Brass with a machine fine finish . They are 20mm diameter and 4mm thickness. Central register hole to ensure that spikes are engaged correct Prevent damage to wood / laminate flooring Excellent for speaker cabinets to ensure even grounding / mass stability for excellent bass performance Can be used in conjunction with adjustable spikes to stabilise / isolate turntables. For delicate surfaces please use our self adhesive felt pads which can be found in our amazon shop. 15mm felt pads for 20mm speaker spike pads 12mm felt pads for 16mm speaker spike pads 100% satisfaction guarantee - If you are not 100% happy with your purchase please just get in contact and we will do our absolute best to put things right.