Kilt pins are used to help give some weight to the front apron, so it will stay in place. They are only meant to be put through the top apron. Do not pin it through the two layers or you will have to unpin and and re-pin it every time you dress causing more wear and tear on your kilt than needed. Many people tend to have plain ones for more causal functions, and more ornate ones for formal occasions, such as a jewelled silver kilt pin. Some often tend to match the kilt pin with the rest of the jewellery. For example, if your buckle and cuff links have a thistle on them, then many would match with a thistle kilt pin.