Might want to be careful with those...
they aren't worth the $6 they cost when they sometimes fail.
Used to be in the tire and wheel industry and saw many failures from those...
three different failure modes for them that are all quite common:
1) low tire pressure, but reading ok tire pressure - on more than one occasion, I have pulled those caps off a completely flat tire, and they still show that there is proper air pressure in them
2) slow leak - they are plastic and plastic isn't so good at holding pressure... with heat especially, the bonds can come loose and cause a slow leak, by the time it is noticed, it is usually too late for the tire
3) catastrophic failure - also on more than one occasion, I have seen the top plastic part completely blown off of the base, causing a complete loss of tire pressure, as fast as air can be let out of a valve
Although these don't happen all the time, it is still a relatively common occurrence. There was a recall a year or two ago regarding one brand of these and the 3rd reason I listed above, however I have seen failures of all different types from different manufacturers.
You are better off, IMO, with just a plain plastic or metal valve cap and checking the pressure once a week or month, than you are with these things...
