An extremely rare refractory metal, rhenium is most often found in superalloys, alloys that are extremely 
durable and resist deformation at high temperatures, such as those used jet turbine engines.
One of the more unique uses for rhenium, however, has been in dart barrels. Rhenium's use in darts began not because of its heat resistance or strength, but because of its density.
Rhenium is amongst the most dense metal elements (it is only surpassed in weight by iridium and platinum), which means that rhenium dart barrels have the highest mass to volume ratio available of any dart. (Actually the barrels are made of a tungsten-rhenium alloy containing about 5% rhenium).
The increased density allows for a sleeker, thinner design that theoretically - although I don't know that it would my game much - leaves more space to hit three treble 20s.
Image: Rhenium-tungsten alloy darts. Copyright © A180 Darts Ltd. www.a180.co.uk
Comments
High density means large mass/volume ratio
You’re right. I’m glad someone is paying attention
Correction made.
Finally there is a household source for rhenium. I hope that I can find some of these darts.
I love my rhenium darts but don’t no what size stem is best. Long stems I hit the trebal 20 but nothing eals short I can hit more but when it comes to scoring, it’s 81 26 85 45 100. And was wondering what over people use???
I have the Rhenium 21 gram “B” barrel dart that I bought on eBAy.
I believe that they are not manufactured anymore and only came in 21 & 22 gram weights and an “A” barrel (smoother knurling) and a “B” barrel (deeper knurling).
The price has come down considerably from the near $100 per set of three, perhaps because they were discontinued. to about $79.00.
I prefer a shorter stem due to their relative light weight and my throwing style.
I am waiting for a delivery of Cosmo Fit-Flights and “In-between” carbon shafts. In-between short and medium although now Fit-Flight uses a scale of 1-8, 1 being Xtra-Short, 8 almost a javelin.
I do like the heavy compact feel of this ‘pencil dart’. It’s only 5 o/o Rhenium, 95 o/o Tungsten. Wolfram is an archaic term for Tungsten, so “95 o/o Wolfram Tungsten” is just that, Tungsten.