The questions are coming in:
100 KPA (inner scale)is one BAR. or 14.7 PSIA at sea level ( outer scale).
Use plumbers' Teflon tape or Pipe thread compound on the gauge's threaded connector.
The gauges at the price I shipped are black unless you buy a very much upscale one from McMaster or buy a cheap gauge elsewhere in chrome and replace the case. The idea was accuracy at a low cost point.
Other smaller gauges 1.5" diameter for use as a full time gauge:
http://www.omega.com/ppt/pptsc.as..._Series&Nav=preg02PGU-15L-30PSI/2BAR In Stock $15.15 Utility pressure gauge with 1 1/2" dial, lower fitting, 0-30 psi outer scale and 0-2 bar inner scale
OR
http://www.mcmaster.com/4000K422
(Same as 4000K717)
Multipurpose Gauge - 2% Mid-Scale Accuracy 1-1/2" Dial, 1/8" NPT Bottom, 0-30 PSI/200 Kpa
In stock at $10.70 Each
There are other sizes.
Use a 1/8th" to ¼"NPT adapter from a home center type store @ ~$1.50
I know of no method of guessing how a threaded connection gauge will face. If it does not face correctly, either get a cheap NPT tap $7-$10 from a home store and rotate it into the adapter with a crescent wrench as much farther as the gauge has to go, or, take it to the local plumbing shop with a pound of coffee for a pourover and show them how far it has to go and ask them to tap it a bit deeper. Hold the adapter in a loop of leather belt in a vise. or because the brass is soft wrap the belt around and use the belt as a strap wrench to tun the adapter with the tap held in a vise.
If you don't like what you have received, ship it
all unmodified back insured USPS Priority Mail and I shall refund all but shipping charges.
Many happy pulls!
Richard