View Full Version : interchangeable parts - inch versus metric

September 03, 2008, 16:25
interchangeable parts - inch versus metric

muzzle device
NO - threads are same pitch but turn opposite ways

YES - although inch requires a breeching washer

gas block
YES - although metric port meets barrel perpendicular, whereas inch meets at angle, also inch block is taller

gas knob

gas knob retaining clip/spring

gas plug

gas piston

gas piston spring

gas tube retaining collar (the part that screws into the receiver)
YES (small issue here - but generally the answer is yes)

front sight

front sight plate
(metric only)

front sight plate spring
(metric only)

front sight retaining scrw
(inch only)


handguard screw
SOMETIMES - depending on source and length

handguard ring

front swivel

upper receiver
YES - (more or less), depending on what you hang on it

lower receiver
YES, if simply installing a complete lower from one type onto another

ejector block



NO unless it is already installed on a bolt

extractor plunger

extractor spring
??? I think so

bolt carrier

firing pin
generally NO -- except the discussions of one-piece and two piece firing pins, and the differing lengths and configurations, give me a brain cramp
Most metric is one-piece, and most inch is two-piece. So that settles the issue for general comparisons

firing pin spring
??? - don't think so - although it may be if a two-piece firing pin is used in a metric rifle.

firing pin retaining pin

rat tail

rat tail spring

rat tail rivet

bolt hold-open
metric fits inch but not vice-versa (inch is fatter)

bolt hold open retaining screw

magazine catch
YES, but be careful of spring length (inch is longer)

magazine catch spring
NO - unless you switch the magazine catch at the same time - inch is longer

rear sight
YES - but heights differ (inch is taller)

rear sight screws

top cover
metric will work on inch - but not vice-versa without bubbafication

trigger axis-pin
??? I think so

hammer axis-pin
??? I think so




hammer spring

hammer plunger

trigger plunger

sear plunger
NO (inch doesn't even have a sear plunger)

sear spring

trigger return spring

hammer spring
NO (inch plunger and spring are hermetically-sealed assembly)

hammer spring shroud

locking plate
NO (inch plate is unitized with lower)

metric fits inch, but inch won't fit metric without modification

recoil springs
YES (both)

recoil spring plunger

recoil spring tube

recoil spring retaining nut

locking shoulder

locking body

locking body plunger
??? I think so

locking lever

locking body spring

locking lever retaining screw
??? I think so



buttplate retaining screw
sometimes sorta (depends on configuration and length)

rear swivel

pistol grip

pistol grip retaining nut
NO (inch has a screw)

pistol grip retaining scrw
NO (metric has a nut)

trigger return plunger retaining plate
(inch only)

pistol grip "popsicle stick"
(inch only)

trigger guard

metric usually fits inch, but not vice versa without modification

magazine followers
disagreement over this issue - most say NO

magazine springs
disagreement over this issue - most say NO

magazine floorplate

September 03, 2008, 16:25
I'm sure I forgot something, and there are a couple gaps in my certainty - indicated by ???

comment as you spot issues

September 05, 2008, 11:27
The rear part of metric and inch two piece firing pins are identical, the front pieces are not. Metric bolt=metric firing pin, inch=inch.

Israeli Selector is another species.

Hammer shroud, spring, and plunger can be used in either lower if replaced as a set. Metric will self disassemble if your inch lower is uncocked when open.

Charging handles, metric in inch needs a spot drilled for the detent. Inch in metric needs to be thinned and receiver or handle modified so it will fold and lock.

June 06, 2009, 21:38
What about carry handles?

Most seem to mention heavy barrel vs standard, and not sure how to identify the HB vs standard.

March 25, 2010, 20:19
So from what I read here, a new pair of metric handguards from DSA will fit my L1A1?

March 21, 2014, 14:58

April 07, 2016, 19:47

December 21, 2016, 09:33
So why did you delete all my corrections?

February 14, 2017, 19:02
Are there bipods from other versions of the FAL firearm platform that won't fit on certain different manufacturers of bipod barrels? Example: Belgian to Imbel, SA to Belgian, etc.
Attention Moderator. Do you want to start another "Sticky" on this subject?

February 14, 2017, 19:17
So why did you delete all my corrections?

No idea what you are talking about Mark.
Nothing of yours has been deleted in this thread.

February 14, 2017, 19:17
What about the interchangeability of bipods between different versions of the FAL that have bipod barrels?
Attention Moderator. Do we need to start another "Sticky" on this subject?

Glad you brought that up.

Thank you for volunteering to write it.

February 15, 2017, 08:14
Corrected - again.

interchangeable parts - L1A1 versus FAL (there is no "metric" and "inch")

major groups - yes.
Complete barreled upper, complete bolt & carrier assembly, complete lower assembly will interchange with the limiting factor being rear sight must match front sight for height. Parts within the assemblies, no.

muzzle device NO, except early RH thread FALs
FAL 9/16x24, LH
L1A1 9/16x24 RH

receiver - yes
except for some differences which can be worked around easily, and which magazine, FAL & L1A1 can be built on either receiver.
differences = ejector block dimensions (mag catch and bolt hold open fit), cocking handle clearance, receiver cover clearance

barrel & gas block no
FAL = 90 degree gas port
L1A1 = 45 degree gas port
some have morphed the two together with various degrees of success. L1A1 uses a breeching washer. Much match rear sight to front sight.

gas regulator -NO
FAL screwed on
L1A1 retained by spring clip

gas regulator adjustment spring - YES

gas plug - NO

gas piston - YES

gas piston spring YES

gas tube support nut - no (the part that screws into the receiver)
L1A1 has clearance for breeching washer and can be used on FAL
FAL has no breeching washer clearance and cannot be used on L1A1.

front sight - NO

front sight plate -NO
(FAL only)

front sight plate spring - NO
(FAL only)

front sight retaining screw - no
(FAL only)

handguards - yes

handguard screw - no
FAL & L1A1 are both #10x32 thread, but the FAL is a larger shaft. Hole in gas block muyst be enlarged.

handguard ring - no
FAL - no clearance for breeching washer

front swivel - sometimes
FAL - parallel sides
L1A1 UK "wings" limit travel
L1A1 Australia - tab on sling band must fit into clearance cut not present on FAL barrels.

ejector block - no
channel for bolt hold open smaller on L1A1.
hole for mag catch spring larger on L1A1

ejector - no
L1A1 ejector block includes fixed ejector
FAL may be fixed or (more common) removeable

complete bolt assembly - yes
firing pin retaining pin, yes.
extractor, spring, plunger -no
firing pin, sprin - no

bolt carrier, bolt carrier rat tail, spring, plunger, axle/rivet - YES

bolt hold-open - no
FAL larger diameter

magazine catch & Spring - no
ejector block spring hole may be enlarged to use larger L1A1 spring on FAL
magazine catch screw - no
ambidextrous feature of l1a1 mag catch requires large head L1A1 screw. May interchange as a catch, spring, screw assembly with appropriate sized spring recess in e4-block

rear sight assemblies - YES
components within the rear sight - no
rear sight screws - yes
rear sight windage spring - yes

receiver cover
L1A1 has tabs FAL does not. FAL will fit L1A1, tabs must be removed on an L1A1 to fit FAL

trigger axis-pin - no
L1A1 smaller
hammer axis-pin - no
L1A1 larger

hammer, trigger, sear -no

hammer strut assembly - yes
parts within hammer strut assembly - no

trigger plunger, sear plunger, trigger spring, sear spring - NO

selector - no
FAL has a limit pin for selector travel
L1A1 has a tab that hits upper receiver to limit travel
either can be modified to work with the other, as axel dimensions are the same

return spring, inner & outer, return spring plunger - yes

recoil spring tube - no
L1A1 larger thread

recoil spring retaining nut
YES, except for early ones for the wood stock L1A1 are not threaded inside for the buttplate screw.

locking shoulder - YES

locking body - YES
L1A1 has flat nose, but they interchange.

locking body plunger - no
fal is round for wasp-waist pin
L1A1 is flat for straight retaining pin.

locking lever - yes

locking body spring - yes

locking lever retaining screw - yes

buttstock, buttplate - no

buttplate retaining screw - yes
all are 1/4x28 - L1A1 comes in 4 different lengths.

rear swivel -NO

pistol grip & grip hardware - NO

trigger guard - NO

magazine - no
FAL will fit L1A1, but with no front support, the front of the mag will droop and cause intermittant feeding malfunctions.

magazine, & magazine components - no
L1A1 spring and follower have different method of retention than FAL. Spring can be used but suboptimal

August 31, 2018, 06:46
On the advice I've reopened this thread about inch/metric differences....my head HURTS! I think I'll just buy a "made" riFal! Thx for ALL the info-pretty good! :beer: