Instruments:
There is not enough space here to present a cataloge of instruments if it is about a wide diversity of music like we can find in Thailand.
Besides the music of the ensembles we find several solo instruments, most of all if we take a closer look at the instruments of the various ethnic minorities living in the actual borders of Thailand.

The following overview only displays instruments that I own in my collection or are basic for the understanding of Thai music - all other instruments are described in the article about the ensembles below.

o the zither Jarakhe
o the panpipe Wot
o the hammered dulcimer Khim
o the mouthorgan Naw
o the harp Tünak of the Karen people                                                                     
o the Subü lute of the Lisu people
o the monochord Pin Pia  
o the lute Sueng      
o the flute Khlui     
o the bamboo reed Pi Phu     
o the fiddle Saw                                                                                       

The solo music is not rare but outweighted by ensemble music. Vocalists often tend to alternate with the ensemble instead of being accompanied, and the real determination of pitches and playing styles is coming from the used aerophones, which we already see in the name "Piphat", indicating the Pi (see below) aerophones as very important. Today sometimes ensembles get mixed up though the instrumentation is clearly defined for each occasion, but sometimes the required players or instruments are not availabe. Most of the ensembles perform seated and play all pieces from memory.

Basically, three major ensembles dominate the music of Thailand: The Piphat, the Mahori and the Khrüang sai.

Besides these three major ensembles, the Malayian influenced  sword fighting ensemble bua loi as well as the boxing ensemble klawn khaek get more and more famous. The Piphat ensemble is a very percussive ensemble, while the Mahori ("instrumental") ensemble can be seen as a smaller Piphat with smaller and additional string instruments; and the Khrüang sai is a string dominated ensemble with at least two fiddles and a zither. All ensembles know additional names regarding their instrumentation and function, for example "ha" (five instruments), "khu"
(all instruments paired) or "yai" (large ensemble with 13 instruments, called "mai khaeng" if played with hard mallets and "mai nuam" if played  with soft mallets). Exceptions are the Piphat mawn, remarkable for the upright gong circle of Mon origin, the Piphat nang hong playing Muslim and Indian tunes and the rarely seen theatre ensemble Piphat dükdanbam.

The instrumentes presented on this page are mainly found in the various ensembles of Thailand. Instruments like the Phin lute actually get electrified, but we also find examples of instruments that root back into ancient times.
Of course, the following list is far away from being complete:

IDIOPHONES:
ching         -   the most important but most unimpressive instrument consists of two identical brass cymbals of 5-6 cm diameter.
chap          -   thin brass cymbals in two sizes: lek (12-14 cm, bound with a string) and yai (23-26 cm, no string)
                       also indicates the dampened striking of the ching cymbal.
krap           -   wooden or brass castagnets, three variations are: khu (bamboo, 40 cm), phuang (brass, 22 cm) and sepha (wood, 21 cm)
Ranaad     -   the main xylophone with bamboo plates and a boat shaped resonating box. Reminds of the Burmese patala and was first
                        mentioned in Thailand in 1826. The three versions are: 21 bamboo plates ranging from G to f1 (ek), the bigger and lower
                        tuned version with 17-18 plates that is only played with soft mallets (thum) and the rare small bronze version (lek).
Khawng    -   Systems of bossed gongs, struck with padden beaters. Knows several forms and shapes, for example the framed gong set
                       of 8 hanging gongs (rang) which reminds of the Javanese bo nang and the Philippines Kulintang, the upright gong circle
                       shaped like an U (mawn) of Mon origin and the famous circle (wong) of 16 (lek) to 18 (yai) gongs, which are 12-17 cm in diameter
                       and tuned in a pentatonic scale,  ranging from D to e1 - a model for students to start studying traditional music, but also
                        providing the core melody (luk khawn) of the ensemble.

Other idiophones include the bornze drums "mahoratük" of the Karen, the Angkalung (Angklung) of Indonesian origin used in schools and the slit drums called  "kraw" which are made by a cut open section of bamboo and can reach sizes of over two meter (krong).

DRUMS:
Taphon        -  A sacred pair of drums placed on a stand and with the smaller drum (22 cm) placed right, the bigger one left (25 cm), a drum that
                          only gets performed in the Piphat ensemble and is played by hands - the Piphat mawn knows a bigger version of 51 cm.
Thon             -  A vase shaped drum reminding of the Persian Dombak or the Arabian Darbuka, played with the right hand while the left
                          covers the open end to modulate the tone, comes in two sizes:  36 cm (chatri) and 38 cm (mahori).
Khaek           -  A drum of 20 cm diameter reminding of the Gendang in Malaysia, forms with the pi chawa the famous Thai boxing ensembles

Other drums include frame drums like the Ramana (26 cm) and the drum circle boeng mang kawk with seven drums hung in a circle, thus reminding us of the Burmese pat waing drum cricle.

AEROPHONES:
Khlui            -   A vertical bamboo block flute with 6-7 playing holes, appearing in three sizes: 36, 45 and 60 cm long, pitched d,c and G
                          The Khmer know a version (khloy) with a membrane covering the thumb hole like with the Chinese Dizi, but more
                          important is the discussion about the position of the playing holes, approximating an equidistant scale.
Pi                   -  A double reed comparable to the Indian Shenai and the Khmer Sralai. Appears in various forms and sizes:
                          nai (40 cm, pitch G, used in Piphat), klang (37 cm, pitch A, used in the shadow puppet theatre), nawk (31 cm, pitched C),
                          or the bamboo version aw (25 cm, used mainly in Cambodia), the metal version chanai (19 cm, rare), the big and heavy
                          mawn of the Mon people (50 cm) and the famous chawa (29 cm, from Java) used in the Thai boxing ensembles.
Trae               -  metal trumpets influenced by the French colonists, played in ceremonies for royal visitors
Sang              -  A long metal horn from India

The diversity of flutes and reeds is to rich to be displayed here, and one should always keep in mind that normally flutes change over a period of time, like we can see in the appearance of plastic flutes instead of bamboo models.

CHORDOPHONES:
Krajappi        -  A 180 cm long 4 stringed lute with 11 frets which is known as "Chapey" in Cambodia and there a part of the narrative style.
                           It reminds also of long neck lutes like the Vietnamese Nguyet and once was used in Mahori ensembles.
Saw                -  The basic fiddle, appears in three basic forms: with three strings (sam sai, tuned A-d-g) or two strings (duang, tuned g-d
                           and the bigger hu, tuned C-g, reminding us of the Chinese Erhu). Spike fiddles like these are common all over Asia and
                           can be found in Malaysia (rebab), Burma (tros), Cambodia (tro) and Vietnam (Nhi).

Other chordohpones are included in the Khrüang sai and Mahori ensembles today, but like the hammered dulcimer Khim, the floor zither Jarakeh or the modern guitar-like lute Phin, most of these instruments are not of Thai origin and represent modern instruments which reflect
new developments and implementations of other origin. Especially the Khim knows many solo traditions today, and it seems somehow ironical that the most famous instrument nowadays in Thailand is from Chinese origin (Yang Qin), like we can also see in the increasing interest in the mouthorgan Khene which maybe originated in Laos.

Please also take a look at my videos on "Youtube" - you will find hundreds of videos with Thai and other instruments...