I just bought three of these.
http://www.ebay.co.uk/itm/FASHION-SILICONE-NURSES-BROOCH-FOB-WATCH-NEW-NURSE-10-COLOURS/121080154631?_trksid=p5197.m1992&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%26asc%3D14%26meid%3D8813555350293312686%26pid%3D100015%26prg%3D1006%26rk%3D1%26sd%3D121080154631%26#ht_903wt_936
I paid about $3 each for them including delivery, the inserts are 1 1/4" across and I used a bit of double sided tape to secure one to the instrument panel..
I figured that If it falls off I have only wasted $3 and can easily replace it..They are stainless steel with a quartz movement, they just squeeze out of the silicone holder and when fitted they look really good...It doesn't matter which color you buy because you can throw away the silicone holder.
John.