The chrysanthemoid (kiku-gata) iron plate with polished surface decorated with arabesque (karakusa) and paulownia (kiri) leaves and flowers in brass, copper and silver flush inlay (hira-zōgan) on both sides. Some of the inlay goes over the edge. Kozuka- and kogai-hitsu-ana are filled with lead plugs. Sekigane of copper. Chrysanthemum and paulownia are the symbols of imperial family. The face is signed: Izumi no Kami to the right of nakago-ana, and Yoshiro on the left; the back is signed Koike Naomasa. His signed work is considered by many experts to have been made-to-order only. The original wooden box (tomobako) with inscription (hakogaki) signed by Dr. Kazutaro Torigoye and dated Showa 39 (1964). The late Muromachi or Momoyama period, 16th century. Dimensions: 89 mm x 84 mm x 3.6 mm; Weight: 170 g. Hakogaki lid: Yoshirō  kikka-gata Hakogaki lid inside: Iron, signed on the omote: Izumi no Kami – Yoshirō; on the ura: Koike Naomasa. Kikka-gata, pronounced maru-mumi, two hitsu-ana, karakusa, and kiri design in brass, silver, and suaka hira-zōgan. Height 8.5 cm, thickness 3.5 mm. Herewith I judge this work as authentic. On a lucky day in July of 1964. Torigoe Kōdō [Kazutarō] + kaō According to Robert Haynes [Catalog #7, 1983; №32, page 42-43] "This full form of the signature is seen very rarely". His example, illustrated in that catalogue, measures: height = 86 mm, thickness at seppa-dai = 3.75 mm and signed Izumi no Kami Yoshiro on the back and Koike Naomasa on the face. The further description of his specimen by Robert Haynes:

"Early signed example of the work of Koike Naomasa. The kiku shape iron plate is well finished. The flush inlay is brass, for the scroll work on both sides, with the leaves and kiri mon in brass, copper and silver with strong detail carving. Some of the inlay goes almost over the edge, which is goishi gata. The large hitsuana are plugged in lead with starburst kokuin surface design. [...]The face is signed in deep bold kanji: Koike Naomasa; the back is signed: Izumi no Kami, on the right and Yoshiro on the left. There are one or two small pieces of inlay missing. Sold by Sotheby London, Oct. 27, 1981, lot 368. Height = 86 mm, thickness (seppa-dai) = 3.75 mm, (edge) = 4 mm."

Another similar example presented at: "Tsuba" by Günter Heckmann, 1995, №T55 — "Designation: Koike Naomasa. Mid Edo, end of the 17th century. Iron, hira-zogan in brass, copper, silver and shakudo, katakiri-bori. Tendrils and leaves. 87.0 x 78.0 x 4.0 mm." Reference: Japanische Schwertzierate by Lumir Jisl, 1967, page. 13. [SV: Actually, his tsuba is signed Izumi no Kami  Yoshiro on the back; and Koike Naomasa on the front, exactly as Robert Haynes's tsuba. Dating this tsuba Mid-Edo, 17th century may be considered a misattribution]. More details regarding the Yoshirō tsuba. 

Iron tsuba of octafoil form with design of rudder (kaji) and lake in openwork (sukashi) outlined with brass wire. Thin plate also decorated with three concentric circular rows of brass dots (nail heads) in ten-zōgan. Center of the plate outlined with the inlaid circular brass wire. Cut-outs for kozuka and kogai probably added later.  Slightly raised rim between the indentations (suki-nokoshi-mimi). The inlaid metal of red-ish hue, so it may be copper, not brass. Sekigane, visible on the NBTHK paper photo, are missing, possibly removed by a previous owner. Muromachi period. Ōnin school. Unsigned. Dimensions: 81.2 mm x 81.8 mm x 2.7 mm. Weight: 79.0 g. Large nakago-ana: 34 mm high and 10 mm wide. NBTHK certificate №455786: Hozon. Note regarding design: it was quite hard to interpret the big oval opening. The first suggestion was 'sea cucubmer', and it was based on a design published by Kazutaro Torigoye [Kodogu and tsuba. International collections not published in my books (Toso Soran), 1978] on page 202: Katchūshi tsuba: Sea cucumber and butterfly. Look and judge yourself: The second suggestion - 'lake' - came from [Iron tsuba. The works of the exhibition "Kurogane no hana", The Japanese Sword Museum, 2014], page 14 №5: Opening on my tsuba looks more like the 'lake'. Also, rudder and lake make more sense than rudder and sea cucumber. At least to me...    

A circular iron tsuba with a design of three monkey toys (kukurizaru) in small openwork (ko-sukashi); the plate further decorated with four rows of brass dot inlay (ten-zogan). The center of the plate and the openings are outlined with brass wire. Copper sekigane. A few dots missing. Muromachi period. Dimensions: 89.0 x 88.2 x 2.9 mm. Kukurizaru was an often used motif on old tsuba. The symbol has two explanations: (1) "upright" monkey, a sort of roly-poly toy, alludes to 'never-ever give up' property of the samurai; (2) monkeys are represented with their hands and feet tied to their back to symbolize self-control. Other examples of the same design:

Iron tsuba of mokkō form decorated with inome (wild boar's eye) in openwork (sukashi) outlined with brass wire. The plate decorated with 3 concentric circular rows of brass dots in ten-zōgan. Center of the plate outlined with the inlaid circular brass wire (sen-zōgan). Some dots and the outline of inome on the face are missing.

Ōnin school. Unsigned. Mid Muromachi period, middle of the 15th century. Dimensions: 72.1 x 71.3 x 2.3 mm.

Iron tsuba of six-lobed (mutsu-mokkō-gata) form, with six wild boar's eye shape (inome) openings (sukashi). Hitsu-ana and the entire perimeter of tsuba have typical for this school raised rim. Lobes are decorated with landscape motifs in low relief carving (sukidashi-bori). On the obverse: A hut under a full moon, Shinto shrine gates (torii) with pines and a full moon, rocks, a large pine tree, and a temple (pagoda) surrounded by rocks and waves. On the reverse: waves, fishing boat, wild gees in flight under full moon, maple, hexagon (tortoiseshell, kikko) with a dot inside and a dot outside (inclusion/exclusion symbol), and chrysanthemum (the last two may be family crests, mon). Kamakura-bori school. Late Muromachi period (1514-1573). Height: 64.2 mm, width: 74.3 mm, Thickness at seppa-dai: 3.2 mm, at rim 2.6 mm. Weight: 62.8 g (light). NBTHK old green certificate №561: Tokubetsu Kicho  - "Extraordinary Work". A look-a-like tsuba can be found at the Compton Collection, part II, pp. 14-15, №17, though his tsuba is more massive (80 x 84 x 4 mm). NBTHK paper says that the motif is Hakkei (八景), i.e. "Eight Views," so several interpretations are possible (the original Chinese ones, Omi Hakkei, etc.).  However, most likely it is the 'Eight views of Omi' (近江八景  - 'Omi Hakkei'). Why the artist selected a 6-lobed form for depicting 8 views remains unclear, and thus we are in our right to raise the question whether the motif is indeed Hakkei. The term Omi hakkei (eight views of Omi) refers to painting or print sets which illustrate life on the shores of Lake Biwa in Omi (now Shiga Prefecture). The model for such paintings came from China, where, from the eleventh century onward, painters had produced eight views of the Hsiao and Hsiang lake areas of Hunan Province. The themes, which follow the original Chinese models, are: geese descending to land, returning fishing boats, clearing rain, a snow-covered evening landscape, the autumn moon, night rain, a temple bell at evening, and the glow of sunset. Japanese artists have also used the eight-theme approach for other parts of country - including cities - and applied it to subject matter other than landscapes. [Merrily Baird. Symbols of Japan. Thematic motifs in art and design. Rizzoli international publications, Inc., 2001, page 308-9]. Japan Encyclopedia by Louis Frédéric also mentions Omi Hakkei as "Eight landscapes of Omi", and states that this theme was often cited in poetry after 1500. It is likely that the tsuba in focus is designed under the influence of the theme popularity in the 16th century. The theme was effectively exploited by prominent ukiyo-e artists Suzuki Harunobu and Utagawa Hiroshige in the 18th and 19th century, respectively. These are the eight scenes of the theme (see Wikipedia):

• Returning sails at Yabase (矢橋の帰帆) - Yabase. Yabase is an old harbour on the east side of the lake. Near the Tokaido, it was used for a shortcut to Otsu by boat.
• Evening glow at Seta (勢多（瀬田）の夕照) - The Chinese Bridge at Seta. The long bridge across the Seta was used by the Tokaido. In the background the "Fuji of Omi", the Mikamiyama. It is just above 400 m, but indeed well visible.
• Autumn moon at Ishiyama (石山の秋月) - Ishiyama Temple. The Ishiyamadera was located on a hillside next to the Seta River. It got his name form the strange rocks on which it is built, partly on supporting beams. A hut at the upper end of the site allows a view of the lake, and the moon.
• Clear breeze at Awazu (粟津の晴嵐) - Awazuhara. Awazu is well known for its pine wood, Awazu-ga-hara.
• Evening bell at Miidera (三井晩鐘) - Mii-dera. Miidera temple was built in the 8th century. Its famous bell is one of the "Three bells of Japan", the other two being those at Byoodo-in, Uji and at Jingoji, Kyoto.
• Evening rain at Karasaki (唐崎の夜雨) - Karasaki Shrine. Karasaki is a small cape with a single large pine tree, a hitsu-matsu.
• Wild geese returning home at Katata (堅田の落雁) - Ukimido. Alighting geese cannot be seen always, however the little temple near Katata in the square hōkyō-style, detached from the lakeside, connected by a bridge. The first part of the name uki is the same as in Ukiyo-e, meaning floating. Midō means temple.
• Evening snow at Hira (比良の暮雪) - Hira Mountains. The Hira mountains on the west side of the lake experience the hard winter, when the winter monsoon brings much snow from the continent.

In any case, as a conservative, I say that it is a landscape motif and a late Muromachi period work, rather than Omi hakkei motif and a mid-Muromachi work.

A very large and very thin iron tsuba of round form decorated with design of formalized butterfly and dragonfly in openwork (sukashi). The characteristics of the plate resemble those of Kamakura period ko-tōshō tsuba. However, the design seems too 'modern' to me, but it's hard to tell; it may be a late Muromachi or Momoyama period work. Tōshō or Ko-Tōshō school (or a Katchushi). Muromachi period. However, Boris Markhasin and Skip Holbrook insist this is a 20th-century machine-made tsuba. Dimensions: 99.6 x 100.5 x 2.1 mm. This is what Jim Gilbert says about old tsuba:

"Traditionally the old iron plate tsuba are classified into Ko Tosho (old sword smith), and Ko Katchushi (old armor maker) styles. It is sometimes difficult to justify attribution of a given tsuba to the Tosho or Katchushi category. Generally guards with raised rims or relatively complex designs tend to be assigned to Katchushi. This is basically a convention we follow out of habit and convenience." [...] "In Token Kai-Shi part six, Articles by Akiyama Kyusaku, Robert Haynes comments: "…from 1300 to 1400 over 150,000 MOUNTED swords were made in Japan for export alone. This means that over four tsuba a day were made for 100 years. This would mean that at least 3000 persons were making nothing but tsuba, let alone all the other fittings needed to complete these swords. With sword smiths, fittings makers and all the other artists need to complete a sword for export, at least 10,000 sword artists were working together, in any one of these hundred years."

Another tsuba of similar design, Tōshō school, is illustrated in this collection; see TSU-0319.2015. Reference to this design can be found in LIB-1359.2017 Japanese Swords and Tsuba from the Professor A. Z. Freeman and the Phyllis Sharpe Memorial collections, Sotheby's, London, Thursday 10 April 1997; p. 18-19, lot № 37: "A Kamakura-bori Tsuba, Momoyama Period. ...pierced with two large formalised butterflies..."  

Iron tsuba of round form decorated with design of sea waves in low relief carving (kebori) and pierced with design of cherry blossom in negative silhouette (in-sukashi) and water wheel in positive silhouette (ji-sukashi). The solid portion of the plate has a shallow groove just before the edge. Copper sekigane. School attribution is unclear. Unsigned. Momoyama period, 16th - 17th century. Dimensions: Height: 70.3 mm, width: 71.1 mm, thickness at seppa-dai: 4.4 mm, at rim 4.1 mm. Provenance: Robert E. Haynes, Mark Weisman. This is what shibuiswords.com says about this tsuba:

"A very unusual iron plate tsuba. The solid plate is carved with waves on both sides. A cherry bloom in sukashi, lower left, and the right third of the plate in openwork with design of a water wheel. The rim with some iron bones. The hitsu-ana is original but the shape may have been slightly changed. One would expect this to be the work of the early Edo period, but the age of the walls of the sukashi would suggest that this is a work of the middle Muromachi period. This must be the forerunner for the Edo examples we see of this type of design." (Haynes)

I managed to find a look-a-like tsuba in Haynes Catalog #5, 1983, pp. 20-21, №44: "Typical later Heianjo brass inlay example. Ca. 1725. Ht. 7 cm., Th. 4.5 mm., $100/200". We see that the  plate design of both tsuba is the same, and the only difference is the trim. It would be logical to assume that both pieces were made at about the same time, rather than 225 years apart. To be fair, let's accept that they were made in Momoyama period.