NcSTAR MAR4S - Manual (Page 3)

Step 3
Take the bottom half of the Quad Rail, and place the
beveled end inside the Delta Ring. Now, while holding
the bottom half of the Quad Rail, press down towards the
Delta Ring. It may be necessary to apply a fair amount of
pressure in order to get the Quad Rail to fit around the
barrel nut. With the Delta Ring depressed, lower the
bottom half of the Quad Rail down towards the barrel,
making sure to insert the small tabs on the front end of
the Quad Rail into the Handguard Cap (See Fig. 4).
Release pressure on the Delta Ring, and allow the bottom
half of the Quad Rail to set in place (See Fig. 5).
Step 4
Now that the rails are in place, begin setting the six
mount screws into their holes. Next, tighten the screws,
while making sure that they are tightened evenly (See
Fig. 6). Do not fully tighten the screws one at a time, as
this may cause damage to the rail. Once the two halves
of the Quad Rail are properly fastened, then it is ready
for use!