FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 7. Aircraft Hardware, Control Cables, and Turnbuckles | 2. Screws | 7-17. Panhead Screws
9/8/98
SECTION 2. SCREWS
AC 43.13-1B
7-14. GENERAL. In general, screws differ
from bolts by the following characteristics.
a. Screws usually have lower material
strength, a looser thread fit, head shapes
formed to engage a screwdriver, and the shank
may be threaded along its entire length without
a clearly defined grip. Screws may be divided
into three basic groups: structural screws, ma
chine screws, and self-tapping screws. Screws
are marked as required by the applicable Army
Navy (AN), National Aerospace Standard
(NAS), or Military Standard (MS) drawing.
Normally a manufacturer places his trademark
on the head of the screw. Several types of
structural screws are available that differ from
the standard structural bolts only in the type of
head.
b. It would be impossible to cover all
screws that are available to the aviation mar
ket; therefore, only the most frequently used
screws will be discussed in this text. Design
specifications are available in MIL-HDBK-5,
or U.S.A.F./Navy T.O.1-1A-8/NAVAIR
01-1A-8, Structural Hardware.
c. Typical screw types are shown in ta
ble 7-11.
7-15. STRUCTURAL SCREWS. NAS502,
NAS503, AN509, NAS220 through NAS227,
and NAS583 through NAS590, may be used
for structural applications, similar to structural
bolts or rivets. These screws are fabricated
from a material with a high-tensile strength
and differ from structural bolts only in the type
of head.
7-16. MACHINE SCREWS. These screws
are available in four basic head styles: flat
head (countersunk), roundhead, fillister, and
socket head.
a. Flathead machine screws (AN505,
AN510, AN507, NAS200, NAS514, NAS517,
and NAS662) are used in countersunk holes
where a flush surface is desired.
b. Roundhead machine screws (AN515
and AN520) are general-purpose screws for
use in nonstructural applications.
c. Fillister head machine screws (AN500
through AN503, AN116901 through
AN116912, AN116913 through AN116924,
AN116962 through AN116990, AN117002
through AN117030, and AN117042 through
AN117070) are general-purpose screws that
may be used as capscrews in light mechanical
applications and are usually drilled for safety
wire.
d. Socket head machine screws
(NAS608 and NAS609) are designed to be
driven into tapped holes by means of internal
wrenches. They may be used in applications
requiring high strength, compactness of as
sembled parts, or sinking of heads below sur
faces into fitted holes.
7-17. PANHEAD SCREWS (NAS600
THROUGH NAS606, NAS610 THROUGH
NAS616, NAS623, AND NAS1402
THROUGH NAS1406). Flathead screws
(MS35188 through MS35203), panhead ma
chine screws (MS35024 through MS35219),
and truss-head screws (AN526) are general-
purpose screws used where head height is not
important.
7-18. SELF-TAPPING SCREWS. The
self-tapping screw taps their own mating
thread when driven into untapped or punched
holes slightly smaller than the diameter of the
screw. Self-tapping machine screws (AN504
and AN530), may be used to attach minor
Par 7-14
Page 7-3